Imaging agents for diagnosis of Parkinson&#39;s disease

ABSTRACT

Generally, the present invention is directed to central nervous system dopamine transporter-imaging agents and methods of use thereof. In certain embodiments, the present invention relates to radiolabeled piperidine derivatives for use as imaging agents in the diagnosis of Parkinson&#39;s disease. Another aspect of the present invention relates to piperidine monoamine transporter ligands, comprising a functional group capable of chelating a radionuclide, e.g., technetium, and methods of use thereof.

RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application forPatent Ser. No. 60/183,996, filed Feb. 22, 2000.

TECHNICAL FIELD

The present invention is directed to central nervous system dopaminetransporter-imaging agents, and more particularly, to labeled piperidinederivatives for use as imaging agents in the diagnosis of Parkinson'sdisease.

BACKGROUND OF THE INVENTION

Each year approximately 50,000 Americans are diagnosed with Parkinson'sdisease with the estimated total cost to the US economy exceeding $5.6billion annually. There exists no known test for Parkinson's Disease(PD) and current diagnosis relies on observations of the symptomsrelating to deteriorating muscular control. With the difficulties inearly diagnosis and no known causes, except for age or head trauma, theneed for improved screening and treatment in our aging populationcontinues to grow. While it has been demonstrated that diseaseprogression can be monitored non-invasively in vivo by PET,^(1,2) theinaccessibility and cost of PET make such screening ineffective. Theavailability of a radiolabeled dopamine transporter (DAT) ligand forimaging with single photon emission computed tomography (SPECT) wouldbring this capability to the majority of the population. Performing suchbrain imaging studies not only creates the possibility to follow thedegeneration rate of the dopaminergic neurons in Parkinson's disease,but also provides an opportunity to estimate therapeutic effects ofputative neuro-protective agents in individual patients.³ Hence, aninexpensive and widely available agent for imaging DAT is warranted.

The development of radiolabeled ligands for SPECT imaging of the DAT hasbeen difficult. Successful imaging of DAT in primates and humans hasbeen demonstrated using several I-123-labeled analogs of the WIN 35,428series of cocaine analogs.⁴⁻⁶ However, the US market has yet to embraceIodine-1 23 to the extent that there exists a commercially reliable andcost effective supply of this isotope. Tc-99m an inexpensive and morereadily available isotope with ideal imaging characteristics for SPECThas enjoyed limited success as a radiolabel for DAT ligands. Kung et al,have demonstrated the technical feasibility of imaging DAT using TRODAT,a Tc-99m labeled tropane analog.^(7,8) While a notable achievement,absolute brain uptake with this agent is very low resulting in less thanideal image quality. Structure activity studies to predict brain uptakewith this series of ligands has proved to be less than reliable,suggesting the molecular size of the ligands is on the threshold forbeing able to cross the blood brain barrier efficiently. Kung et al haverecently reported the dramatic effects of changes in the length of thecarbon spacer unit in a tropane series of Tc-99m complexes.⁹ Increasingthe spacer length between the chelate and the tropane moeity from one totwo carbons, while maintaining good transporter binding, resulted inlittle if any brain accumulation.

The National Parkinson's Foundation estimates that 1.5 million Americansare affected by Parkinson's disease (PD). While it is important torealize that PD is not a fatal disease, it is a crippling, degenerativedisease with no cure. PD is a slowly progressive disease that affects asmall area of cells located in the area of the brain known as thesubstantia nigra. The degeneration of these cells causes a reduction ina vital neurotransmitter involved in muscle activity (among otherfunctions) called dopamine. The lack of dopamine causes a wide range ofmuscle misfunction but the four primary symptoms are tremors, rigidity,bradykinesia (slowness of movement) and postural instability. Thedisease is generally considered to target older adults, affecting 1 outof every 100 people over the age of 60.

Currently there is no known test available to diagnose a person withParkinson's. The physician has to observe the symptoms until it isapparent that Parkinson's disease is present. Even with an experiencedphysician, an early, accurate diagnosis is difficult, especially withthe many different forms of the disease, all treated with slightlydifferent medications. The treatment of PD (the most common form ofParkinsonism) includes a delicate balance of medications, (usually theanticholinergic amantadine to start, follow by levodopa with cabidopa,Selegiline™, Bomocriptine™, or Perogolide™), allied health interventions(physical, occupational, and speech therapies) as well as newexperimental procedures (thalamotomy to relieve tremors, Diacrin's fetalcell implants-NeuroCell™, or Guilford's neuroimmunophilin technology¹¹).The list of medications for PD is extensive with all of the drugcombinations possessing advantages and disadvantages. Evaluation isusually done on an individual basis in an attempt to minimize thepotential side effects which include nausea, low blood pressure,involuntary movements, and restlessness, to name a few. The diseasemanagement is made more complex when one takes into account the“wearing-off” phenomenon and the “on-off” effects which commonly occurwith these medications. With numerous drug combinations currentlyemployed, countless new drugs coming through clinical trials (i.e. newdopamine agonists, Requip™ and Mirapex™), and the expense of newimplantation procedures, it would be a great asset to be able toevaluate these potential treatments.

SUMMARY OF THE INVENTION

Generally, the present invention is directed to central nervous systemdopamine transporter-imaging agents and methods of use thereof. Incertain embodiments, the present invention relates to radiolabeledpiperidine derivatives for use as imaging agents in the diagnosis ofParkinson's disease. Another aspect of the present invention relates topiperidine monoamine transporter ligands, comprising a functional groupcapable of chelating a radionuclide, e.g., technetium, and methods ofuse thereof.

DETAILED DESCRIPTION OF THE INVENTION

The main focus of our attention addresses the opportunity to improvedetection and management of PD, we realize the other potentialapplications of our technology. Two other large potential marketsconcern cocaine abuse monitoring¹² and attention deficit hyperactivitydisorders (ADHD/ADD). According to the National ADD Association millionsof children (4-6% of the US population) are treated, and manyovertreated, for the complex conditions of ADHD/ADD. The diagnosticcriteria are lengthy and complex, often leading parents and doctors toclinically erroneous conclusions. We believe a definitive test wouldminimize the confusion, decrease unnecessary drug use, guide appropriatetreatment, and monitor existing medications of the commonly prescribedRitalin™, Dexedrine™, and Adderall™. The recent correlation establishedbetween ADD and mutations of the dopamine transporter gene¹³ furtherdemonstrates the need for a DAT-imaging agent.

One approach to developing new method for treatment of Parkinson'sDisease involves investigating the piperidine nucleus, while maintainingthe functional integrity of the system and the established chemistry ofthe N₂S₂ chelator. Based on our proprietary work we have developed theability to rationally design DAT, SERT, and NET selective ligands byemploying different isomeric forms, or other synthetic modifications.¹⁰Our proprietary position allows us to build upon the many recentsuccesses in the field. Herein, we propose to synthesize and label aseries of novel piperidine monoamine transporter ligands withtechnetium-99m, prepare the corresponding rhenium analogs, analyze theirin vitro pharmacology, examine the in vivo localization properties, andevaluate their potential as specific tracers for the dopamine transportsystem. The new technetium imaging agents would improve initialdiagnosis, as well as track the effects of potential therapeuticregiments in PD management.

In particular, one approach is to synthesize a series of novelpiperidine monoamine transporter ligands, including separation andpurification of all cis/trans isomers. Then prepare the correspondingrhenium-piperidine analogs, including separation, purification andstructural identification of all syn/anti isomers. Subsequently, invitro pharmacological studies can be performed on all piperidine ligandsand the rhenium complexes. Thereafter, the 99mTc labeled versions ofhigh affinity binding compounds defined in specific aim 3 can beprepared. Characterization of the technetium-labeled complexes by HPLC,and assessment of the complexes for their stability as a function oftime and concentration, in buffer at physiological pH, and in humanplasma and serum component may also be done Evaluation of the^(99m)Tc-complexes for brain uptake by performing in vivo rat studiesmay further be performed.

During this approach, the synthesis of the N₂S₂ derivatized piperidineligands will be conducted along with the development of the Re/Tc-99mchemistry, analytical methods, and labeling techniques. The rheniumcompounds will be prepared isomerically pure, to determine thestructural identification, as well as the in vitro pharmacologicalprofiles. Having assessed the initial rhenium compounds for selectivityof monoamine transporter binding, we will begin to develop the ^(99m)Tcchemistry of the more promising ligands. Selection of lead compoundswill be based on selectivity for the dopamine transporter versus theserotonin or norepinephrine transporter. The technetium-99m congenerswill be evaluated initially for radiochemical purity and stability.Next, we will perform rat biodistribution studies, for assessment ofbrain uptake and retention analysis in the presence and absence of theDAT binding agent CFT. The sum of these endeavors will allow us todetermine with reasonable certainty the feasibility of our approach forthe development of DAT specific ligand for imaging. The results of theinitial series can also serve to guide the synthesis of subsequentseries of potential ^(99m)Tc agents.

Once the above approach has been accomplished, the following approachmay be pursued, for instance, in vivo imaging studies in non-humanprimates. In this approach, the following may be carried out: (i)validation of regio-selective accumulation (substantia nigra) innon-human primate models using Tc-99m-complexes selected from specificaim 4 and single photon emission computed tomography (SPECT), (ii)determination of in vivo transporter selectivity by pharmacologicalchallenge in non-human primates using transporter selective agents andsingle photon emission computed tomography (SPECT), and (iii) evaluationof the ability of the lead Tc-99m complex to image the “disease state”in a non-human primate as exemplified by unilateral lesions in thesubstantia nigra induced by the neurotoxin, MPTP. Subsequently, a “kit”for the preparation of the Tc-99m complex of the lead compound may bedeveloped, and the radiation dosimetry of the Tc-99m complex of the leadcompound may be assessed. Thereafter, the synthesis of the lead compoundmay be scaled up for: (i)PK and metabolism studies, (ii) assessment ofthe toxicity of the lead compound in two animal species, and (iii)expanded pharmacological studies of the Re-complex of the lead compound.Initiation of IND application preparation may be started.

Early diagnosis of PD is critical for the treatment and successfulmanagement of the disease. To address this issue we propose thedevelopment of our patented complexes into new easy to label^(99m)Tc-piperidine CNS imaging agents. Preparation of Tc-99m-CNSimaging agents would constitute a significant diagnostic and commercialopportunity in the ongoing battle against CNS related diseases such asParkinson's disease.

Tc-99m, the most commonly used radionuclide in Nuclear Medicine,combines desirable physical properties with a 6 hr half-life and a140-KeV gamma energy (85% as gamma photons) and widespread availability,since it can readily be eluted from molybdenum generators.²³ More than85% of the radiotracers currently employed are labeled with Tc-99m.²⁴These compelling criteria make Tc-99m the radionuclide of choice toradiolabel our series of piperidine ligands for targeting the DAT withSPECT.

There is a clear need for clinicians to be able to continually monitorthe brain's DAT receptors in patients, to gather more information on (1)the etiopathogenesis, i.e., the cascade of events that ultimately leadsto degeneration of the dopaminergic neurons, and (2) brain imagingmethods, to estimate the extent of the degeneration of the dopaminergicneurons in the patient. This is not only important for the earlydiagnosis, but will also allow to monitor the effectiveness of allegedneuroprotective compounds on a prolonged basis. The development of arapid non-invasive method to identify dopamine receptor activity iscrucial to the understanding of PD and improving its diagnosis andtreatment.

There is developed a method for preparing the cis and trans isomers of^(99m)Tc-piperidine complexes as radio probes for SPECT. Based on ourprevious work involving the three carbon spacer piperidinederivatives,²⁵ which demonstrated high binding affinities for therhenium complexes at the DAT, we intend to explore other analogs. Thecomplexes showed high binding affinities with the K_(i) values rangingfrom 43-96 nM (using binding assays and [³H]mazindol as the radioligand)but poor brain uptake. Combining our extensive SAR library with the workof Kung and coworkers^(8,9) (where reduction of the carbon tetherimproved brain uptake), leads us to believe that our piperidine basedsystem can maintain the successes of the past while improving upon theshortcomings, most notably brain uptake. Our system incorporates thecocaine-like functionality, the pendant N₂S₂ chelation off the2β-position, and the carbon tether between the piperidine and N₂S₂moiety. Moreover, our new complexes will be well under the molecularweight cutoff of the blood-brain-barrier, using the smaller chemicalentity piperidine and a one carbon tether to the chelator, allowing forimproved brain uptake.

In regards to the chelation of the metal center (Tc or Re) to thepiperidine derivatives, keeping in mind the criteria of stability,predictability, neutrality, and very little perturbation on the system,we utilize the well established N₂S₂ system to provide a robust, neutralmetal(V)-oxo core. We propose synthesizing a pendant N₂S₂ core. Whereasin the past the N₂S₂ derivatives were prepared without regard to chargepotential, we have specifically designed our N₂S₂ chelator to possess aformal 3-charge. Therefore, upon addition of the metal-oxo (3+) core,the overall charge remains predictably neutral. Using the neutraldiaminodithiol analogs, of the type shown in schemes 1-4, has a numberof advantages: a) the piperidine moiety is free and remote from theTc-99m chelation site, b) the product is neutral and is expected toretain the general properties of a cocaine analog, c) derivatives ofdiaminodithiol have proven to be good ligands for chelating Tc-99m atroom temperature with high radiochemical yield and radiochemical purity,d) the ligand core keeps the metal in a favored +5 oxidation state, andfinally e) the size of the Tc-99m-diaminodithio chelate is similar tothat of the phenyl group,²⁶ which should not be detrimental to thebinding. Another advantage of using this chelating strategy is that theN₂S₂ position on the molecule can be altered if necessary in order todetermine its optimal location.

We have recently prepared the initial analog in this series via theroute shown below in Scheme 1. This synthesis commenced with thepiperidine ester 1, that is readily prepared from arecoline in two stepsas reported in the literature.⁸ The ester was hydrolysed and theresulting acid was then converted to the corresponding acid chloride 2with oxalyl chloride in dichloromethane. Initial attempts to acylate theprotected N₂S₂ chelate directly with 2 failed.

Therefore, we turned our attention toward the stepwise construction ofthe N₂S₂ chelate on the piperidine pharmacophore. Reaction of the acidchloride 2 with the protected amine 3 readily afforded the correspondingamide 4. Reduction with borane in THF (to afford 5) and alkylation with6 resulted in the fully protected amidoamino ligand 7. The reduction ofthe amido functionality with borane in THF yielded the diaminodithiopiperidine 8. The p-methyoxybenzyl protection groups were removed bytreatment with mercury (II) acetate in TFA to afford the desired N₂S₂ligand 9. This ligand was characterized by ¹H NMR.

The first of the piperidine-DAT ligands was successfully labeled withTc-99m by a trans chelation reaction with Tc-99m gluconate. The productwas extracted into ethyl acetate and evaluated by HPLC: Hamilton PRP-1column eluted with dimethylglutamic acid buffer and acetonitrile. Themethod applied was a gradient from 10-60% acetonitrile. In the HPLCsystem used the ^(99m)Tc-piperidine complex eluted at 13 minutes whereasthe precursor eluted at 3 minutes. Radiochemical yield was ˜50%, withradiochemical purity >95%.

While the main focus of our attention addresses the opportunity toimprove detection and management of PD, we realize the other potentialapplications of our technology. Two other large potential marketsconcern cocaine abuse monitoring¹² and attention deficit hyperactivitydisorders (ADHD/ADD). According to the National ADD Association millionsof children (4-6% of the US population) are treated, and manyovertreated, for the complex conditions of ADHD/ADD. The diagnosticcriteria are lengthy and complex, often leading parents and doctors toclinically erroneous conclusions. We believe a definitive test wouldminimize the confusion, decrease unnecessary drug use, guide appropriatetreatment, and monitor existing medications of the commonly prescribedRitalin™, Dexedrine™, and Adderall™. The recent correlation establishedbetween ADD and mutations of the dopamine transporter gene¹³ furtherdemonstrates the need for a DAT-imaging agent.

Neurotransmitter receptors and transporters are currently explored usingpositron emission tomography (PET). A recent study indicated that thenormal ≧85% loss in dopamine innervation to the striatum necessary forclinical symptoms of PD, 50-60% reduction in dopaminergic tone can bedetected using PET ligands [¹¹C] 2β-carbomethoxy-3-β-aryltropane and[¹⁸F] 6-fluoro-DOPA. In recent years, imaging of CNS dopaminetransporters using positron emission tomography (PET) and single-photonemission computed tomography (SPECT) has been demonstrated. Most of theradio pharmaceuticals that have been employed for the noninvasivemeasurement of dopamine transporter sites are based on the structure ofthe classical reuptake inhibitor, cocaine.¹⁴ Cocaine itself has beenused as a PET ligand and as expected concentrates in the basal gangiawhere dopamine terminal density is high.¹⁵ Cocaine analogs with higherbinding affinity for dopamine transporter sites and more favorablepharmacokinetic properties (due to slower metabolism) have beendeveloped. Several of these ligands include [¹¹C] CFT(2β-carbomethoxy-3β-(4-fluorophenyl)tropane)¹⁶ and [¹¹C]methylphenidate¹⁷ for PET, and [¹²³I]β-CIT(2β-carbomethoxy-3β-(4-iodo-phenyl)tropane¹⁸, [¹²³I]IPT(N-(3-iodopropen-2-yl)-2β-carbomethoxy-3β-(4-chlorophenyl)tropane)¹⁹ and[^(99m)Tc]TRODAT-1²⁰ for SPECT imaging. While PET/SPECT scanning iscurrently the scientists best tool in potentially leading to improvedtreatment of Parkinson's disease, the present methods have shortcomings.The operation of PET requires access to a cyclotron, with cost andcomplexity precluding wide application at this time. The iodinatedligands, while proven to work, currently suffer from the markets lack ofacceptance of I-123 as a viable tracer. Meanwhile, the brain uptake ofthe Tc-99m-SPECT complexes seriously limit their effectiveness. Otherproblems have also occurred in regards to the transporter selectivity ofstill other compounds.^(21,22)

Compounds and Methods of the Present Invention

In certain embodiments, a compound of the present invention isrepresented by A:

wherein

-   -   X represents O or (H)₂;    -   R represents H, alkyl, alkoxyl, alkylamino, aryl, heteroaryl,        aralkyl, heteroaralkyl, acyl, alkoxycarbonyl, or        alkylaminocarbonyl;    -   R₂ represents H;    -   R₃ represents optionally substituted aryl or heteroaryl;    -   R₄ represents H;    -   R₅ represents independently for each occurrence H, alkyl,        alkoxyl, alkylamino, aryl, heteroaryl, aralkyl, heteroaralkyl,        acyl, alkoxycarbonyl, or alkylaminocarbonyl; and    -   n is 0, 1, or 2.

In certain embodiments, a compound of the present invention isrepresented by A and the attendant definitions, wherein X represents O.

In certain embodiments, a compound of the present invention isrepresented by A and the attendant definitions, wherein R representsalkyl.

In certain embodiments, a compound of the present invention isrepresented by A and the attendant definitions, wherein R₃ representsoptionally substituted phenyl.

In certain embodiments, a compound of the present invention isrepresented by A and the attendant definitions, wherein R₅ represents Hor aralkyl.

In certain embodiments, a compound of the present invention isrepresented by A and the attendant definitions, wherein n is 1.

In certain embodiments, a compound of the present invention isrepresented by A and the attendant definitions, wherein X represents O;and R represents alkyl.

In certain embodiments, a compound of the present invention isrepresented by A and the attendant definitions, wherein X represents O;and R₃ represents optionally substituted phenyl.

In certain embodiments, a compound of the present invention isrepresented by A and the attendant definitions, wherein X represents O;and R₅ represents independently for each occurrence H or aralkyl.

In certain embodiments, a compound of the present invention isrepresented by A and the attendant definitions, wherein X represents O;and n is 1.

In certain embodiments, a compound of the present invention isrepresented by A and the attendant definitions, wherein X represents O;R represents alkyl; and R₃ represents optionally substituted phenyl.

In certain embodiments, a compound of the present invention isrepresented by A and the attendant definitions, wherein X represents O;R represents alkyl; and R₅ represents independently for each occurrenceH or aralkyl.

In certain embodiments, a compound of the present invention isrepresented by A and the attendant definitions, wherein X represents O;R represents alkyl; R₃ represents optionally substituted phenyl; and R₅represents independently for each occurrence H or aralkyl.

In certain embodiments, a compound of the present invention isrepresented by A and the attendant definitions, wherein X represents O;R represents methyl; R₃ represents 4-chlorophenyl; R₅ representsindependently for each occurrence H or 4-methoxybenzyl; and n is 1.

In certain embodiments, a compound of the present invention isrepresented by B:

wherein

-   -   X represents O or (H)₂;    -   R represents H, alkyl, alkoxyl, alkylamino, aryl, heteroaryl,        aralkyl, heteroaralkyl, acyl, alkoxycarbonyl, or        alkylaminocarbonyl;    -   R₂ represents H;    -   R₃ represents H;    -   R₄ represents optionally substituted aryl or heteroaryl;    -   R₅ represents independently for each occurrence H, alkyl,        alkoxyl, alkylamino, aryl, heteroaryl, aralkyl, heteroaralkyl,        acyl, alkoxycarbonyl, or alkylaminocarbonyl; and    -   n is 0, 1, or 2.

In certain embodiments, a compound of the present invention isrepresented by B and the attendant definitions, wherein X represents O.

In certain embodiments, a compound of the present invention isrepresented by B and the attendant definitions, wherein R representsalkyl.

In certain embodiments, a compound of the present invention isrepresented by B and the attendant definitions, wherein R₄ representsoptionally substituted phenyl.

In certain embodiments, a compound of the present invention isrepresented by B and the attendant definitions, wherein R₅ represents Hor aralkyl.

In certain embodiments, a compound of the present invention isrepresented by B and the attendant definitions, wherein n is 1.

In certain embodiments, a compound of the present invention isrepresented by B and the attendant definitions, wherein X represents O;and R represents alkyl.

In certain embodiments, a compound of the present invention isrepresented by B and the attendant definitions, wherein X represents O;and R₄ represents optionally substituted phenyl.

In certain embodiments, a compound of the present invention isrepresented by B and the attendant definitions, wherein X represents O;and R₅ represents independently for each occurrence H or aralkyl.

In certain embodiments, a compound of the present invention isrepresented by B and the attendant definitions, wherein X represents O;and n is 1.

In certain embodiments, a compound of the present invention isrepresented by B and the attendant definitions, wherein X represents O;R represents alkyl; and R₄ represents optionally substituted phenyl.

In certain embodiments, a compound of the present invention isrepresented by B and the attendant definitions, wherein X represents O;R represents alkyl; and R₅ represents independently for each occurrenceH or aralkyl.

In certain embodiments, a compound of the present invention isrepresented by B and the attendant definitions, wherein X represents O;R represents alkyl; R₄ represents optionally substituted phenyl; and R₅represents independently for each occurrence H or aralkyl.

In certain embodiments, a compound of the present invention isrepresented by B and the attendant definitions, wherein X represents O;R represents methyl; R₄ represents 4-chlorophenyl; R₅ representsindependently for each occurrence H or 4-methoxybenzyl; and n is 1.

In certain embodiments, a compound of the present invention isrepresented by C:

wherein

-   -   X represents O or (H)₂;    -   R represents H, alkyl, alkoxyl, alkylamino, aryl, heteroaryl,        aralkyl, heteroaralkyl, acyl, alkoxycarbonyl, or        alkylaminocarbonyl;    -   R₁ represents H;    -   R₃ represents optionally substituted aryl or heteroaryl;    -   R₄ represents H;    -   R₅ represents independently for each occurrence H, alkyl,        alkoxyl, alkylamino, aryl, heteroaryl, aralkyl, heteroaralkyl,        acyl, alkoxycarbonyl, or alkylaminocarbonyl; and    -   n is 0, 1, or 2.

In certain embodiments, a compound of the present invention isrepresented by C and the attendant definitions, wherein X represents O.

In certain embodiments, a compound of the present invention isrepresented by C and the attendant definitions, wherein R representsalkyl.

In certain embodiments, a compound of the present invention isrepresented by C and the attendant definitions, wherein R₃ representsoptionally substituted phenyl.

In certain embodiments, a compound of the present invention isrepresented by C and the attendant definitions, wherein R₅ represents Hor aralkyl.

In certain embodiments, a compound of the present invention isrepresented by C and the attendant definitions, wherein n is 1.

In certain embodiments, a compound of the present invention isrepresented by C and the attendant definitions, wherein X represents O;and R represents alkyl.

In certain embodiments, a compound of the present invention isrepresented by C and the attendant definitions, wherein X represents O;and R₃ represents optionally substituted phenyl.

In certain embodiments, a compound of the present invention isrepresented by C and the attendant definitions, wherein X represents O;and R₅ represents independently for each occurrence H or aralkyl.

In certain embodiments, a compound of the present invention isrepresented by C and the attendant definitions, wherein X represents O;and n is 1.

In certain embodiments, a compound of the present invention isrepresented by C and the attendant definitions, wherein X represents O;R represents alkyl; and R₃ represents optionally substituted phenyl.

In certain embodiments, a compound of the present invention isrepresented by C and the attendant definitions, wherein X represents O;R represents alkyl; and R₅ represents independently for each occurrenceH or aralkyl.

In certain embodiments, a compound of the present invention isrepresented by C and the attendant definitions, wherein X represents O;R represents alkyl; R₃ represents optionally substituted phenyl; and R₅represents independently for each occurrence H or aralkyl.

In certain embodiments, a compound of the present invention isrepresented by C and the attendant definitions, wherein X represents O;R represents methyl; R₃ represents 4-chlorophenyl; R₅ representsindependently for each occurrence H or 4-methoxybenzyl; and n is 1.

In certain embodiments, a compound of the present invention isrepresented by D:

wherein

-   -   X represents O or (H)₂;    -   R represents H, alkyl, alkoxyl, alkylamino, aryl, heteroaryl,        aralkyl, heteroaralkyl, acyl, alkoxycarbonyl, or        alkylaminocarbonyl;    -   R₁ represents H;    -   R₃ represents H;    -   R₄ represents optionally substituted aryl or heteroaryl;    -   R₅ represents independently for each occurrence H, alkyl,        alkoxyl, alkylamino, aryl, heteroaryl, aralkyl, heteroaralkyl,        acyl, alkoxycarbonyl, or alkylaminocarbonyl; and    -   n is 0, 1, or 2.

In certain embodiments, a compound of the present invention isrepresented by D and the attendant definitions, wherein X represents O.

In certain embodiments, a compound of the present invention isrepresented by D and the attendant definitions, wherein R representsalkyl.

In certain embodiments, a compound of the present invention isrepresented by D and the attendant definitions, wherein R₄ representsoptionally substituted phenyl.

In certain embodiments, a compound of the present invention isrepresented by D and the attendant definitions, wherein R₅ represents Hor aralkyl.

In certain embodiments, a compound of the present invention isrepresented by D and the attendant definitions, wherein n is 1.

In certain embodiments, a compound of the present invention isrepresented by D and the attendant definitions, wherein X represents O;and R represents alkyl.

In certain embodiments, a compound of the present invention isrepresented by D and the attendant definitions, wherein X represents O;and R₄ represents optionally substituted phenyl.

In certain embodiments, a compound of the present invention isrepresented by D and the attendant definitions, wherein X represents O;and R₅ represents independently for each occurrence H or aralkyl.

In certain embodiments, a compound of the present invention isrepresented by D and the attendant definitions, wherein X represents O;and n is 1.

In certain embodiments, a compound of the present invention isrepresented by D and the attendant definitions, wherein X represents O;R represents alkyl; and R₄ represents optionally substituted phenyl.

In certain embodiments, a compound of the present invention isrepresented by D and the attendant definitions, wherein X represents O;R represents alkyl; and R₅ represents independently for each occurrenceH or aralkyl.

In certain embodiments, a compound of the present invention isrepresented by D and the attendant definitions, wherein X represents O;R represents alkyl; R₄ represents optionally substituted phenyl; and R₅represents independently for each occurrence H or aralkyl.

In certain embodiments, a compound of the present invention isrepresented by D and the attendant definitions, wherein X represents O;R represents methyl; R₄ represents 4-chlorophenyl; R₅ representsindependently for each occurrence H or 4-methoxybenzyl; and n is 1.

In certain embodiments, a compound of the present invention isrepresented by E:

wherein

-   -   X represents O or S;    -   Y represents O or S;    -   R represents H, alkyl, alkoxyl, alkylamino, aryl, heteroaryl,        aralkyl, heteroaralkyl, acyl, alkoxycarbonyl, or        alkylaminocarbonyl;    -   R₂ represents H;    -   R₃ represents optionally substituted aryl or heteroaryl;    -   R₄ represents H;    -   R₅ represents H, alkyl, alkoxyl, alkylamino, aryl, heteroaryl,        aralkyl, heteroaralkyl, acyl, alkoxycarbonyl, or        alkylaminocarbonyl;    -   m is 1 or 2; and    -   n is 0, 1,or 2.

In certain embodiments, a compound of the present invention isrepresented by E and the attendant definitions, wherein X represents O.

In certain embodiments, a compound of the present invention isrepresented by E and the attendant definitions, wherein Y represents O.

In certain embodiments, a compound of the present invention isrepresented by E and the attendant definitions, wherein R representsalkyl.

In certain embodiments, a compound of the present invention isrepresented by E and the attendant definitions, wherein R₃ representsoptionally substituted phenyl.

In certain embodiments, a compound of the present invention isrepresented by E and the attendant definitions, wherein R₅ represents H,alkyl, or aralkyl.

In certain embodiments, a compound of the present invention isrepresented by E and the attendant definitions, wherein m is 1.

In certain embodiments, a compound of the present invention isrepresented by E and the attendant definitions, wherein n is 1.

In certain embodiments, a compound of the present invention isrepresented by E and the attendant definitions, wherein X represents O;and Y represents O.

In certain embodiments, a compound of the present invention isrepresented by E and the attendant definitions, wherein X represents O;and R represents alkyl.

In certain embodiments, a compound of the present invention isrepresented by E and the attendant definitions, wherein X represents O;and R₃ represents optionally substituted phenyl.

In certain embodiments, a compound of the present invention isrepresented by E and the attendant definitions, wherein X represents O;and R₅ represents H, alkyl, or aralkyl.

In certain embodiments, a compound of the present invention isrepresented by E and the attendant definitions, wherein X represents O;and m is 1.

In certain embodiments, a compound of the present invention isrepresented by E and the attendant definitions, wherein X represents O;and n is 1.

In certain embodiments, a compound of the present invention isrepresented by E and the attendant definitions, wherein X represents O;Y represents O; R represents alkyl; and R₃ represents optionallysubstituted phenyl.

In certain embodiments, a compound of the present invention isrepresented by E and the attendant definitions, wherein X represents O;Y represents O; R represents alkyl; and R₅ represents H, alkyl, oraralkyl.

In certain embodiments, a compound of the present invention isrepresented by E and the attendant definitions, wherein X represents O;Y represents O; R represents alkyl; R₃ represents optionally substitutedphenyl; and R₅ represents H, alkyl, or aralkyl.

In certain embodiments, a compound of the present invention isrepresented by E and the attendant definitions, wherein X represents O;Y represents O; R represents methyl; R₃ represents 4-chlorophenyl; R₅represents ethyl; m is 1; and n is 1.

In certain embodiments, a compound of the present invention isrepresented by F:

wherein

-   -   X represents O or S;    -   Y represents O or S;    -   R represents H, alkyl, alkoxyl, alkylamino, aryl, heteroaryl,        aralkyl, heteroaralkyl, acyl, alkoxycarbonyl, or        alkylaminocarbonyl;    -   R₂ represents H;    -   R₃ represents H;    -   R₄ represents optionally substituted aryl or heteroaryl;    -   R₅ represents H, alkyl, alkoxyl, alkylamino, aryl, heteroaryl,        aralkyl, heteroaralkyl, acyl, alkoxycarbonyl, or        alkylaminocarbonyl;    -   m is 1 or 2; and    -   n is 0, 1, or 2.

In certain embodiments, a compound of the present invention isrepresented by F and the attendant definitions, wherein X represents O.

In certain embodiments, a compound of the present invention isrepresented by F and the attendant definitions, wherein Y represents O.

In certain embodiments, a compound of the present invention isrepresented by F and the attendant definitions, wherein R representsalkyl.

In certain embodiments, a compound of the present invention isrepresented by F and the attendant definitions, wherein R₄ representsoptionally substituted phenyl.

In certain embodiments, a compound of the present invention isrepresented by F and the attendant definitions, wherein R₅ represents H,alkyl, or aralkyl.

In certain embodiments, a compound of the present invention isrepresented by F and the attendant definitions, wherein m is 1.

In certain embodiments, a compound of the present invention isrepresented by F and the attendant definitions, wherein n is 1.

In certain embodiments, a compound of the present invention isrepresented by F and the attendant definitions, wherein X represents O;and Y represents O.

In certain embodiments, a compound of the present invention isrepresented by F and the attendant definitions, wherein X represents O;and R represents alkyl.

In certain embodiments, a compound of the present invention isrepresented by F and the attendant definitions, wherein X represents O;and R₄ represents optionally substituted phenyl.

In certain embodiments, a compound of the present invention isrepresented by F and the attendant definitions, wherein X represents O;and R₅ represents H, alkyl, or aralkyl.

In certain embodiments, a compound of the present invention isrepresented by F and the attendant definitions, wherein X represents O;and m is 1.

In certain embodiments, a compound of the present invention isrepresented by F and the attendant definitions, wherein X represents O;and n is 1.

In certain embodiments, a compound of the present invention isrepresented by F and the attendant definitions, wherein X represents O;Y represents O; R represents alkyl; and R₄ represents optionallysubstituted phenyl.

In certain embodiments, a compound of the present invention isrepresented by F and the attendant definitions, wherein X represents O;Y represents O; R represents alkyl; and R₅ represents H, alkyl, oraralkyl.

In certain embodiments, a compound of the present invention isrepresented by F and the attendant definitions, wherein X represents O;Y represents O; R represents alkyl; R₄ represents optionally substitutedphenyl; and R₅ represents H, alkyl, or aralkyl.

In certain embodiments, a compound of the present invention isrepresented by F and the attendant definitions, wherein X represents O;Y represents O; R represents methyl; R₄ represents 4-chlorophenyl; R₅represents ethyl; m is 1; and n is 1.

In certain embodiments, a compound of the present invention isrepresented by G:

wherein

-   -   X represents O or S;    -   Y represents O or S;    -   R represents H, alkyl, alkoxyl, alkylamino, aryl, heteroaryl,        aralkyl, heteroaralkyl, acyl, alkoxycarbonyl, or        alkylaminocarbonyl;    -   R₁ represents H;    -   R₃ represents optionally substituted aryl or heteroaryl;    -   R₄ represents H;    -   R₅ represents H, alkyl, alkoxyl, alkylamino, aryl, heteroaryl,        aralkyl, heteroaralkyl, acyl, alkoxycarbonyl, or        alkylaminocarbonyl;    -   m is 1 or 2; and    -   n is 0, 1, or 2.

In certain embodiments, a compound of the present invention isrepresented by G and the attendant definitions, wherein X represents O.

In certain embodiments, a compound of the present invention isrepresented by G and the attendant definitions, wherein Y represents O.

In certain embodiments, a compound of the present invention isrepresented by G and the attendant definitions, wherein R representsalkyl.

In certain embodiments, a compound of the present invention isrepresented by G and the attendant definitions, wherein R₃ representsoptionally substituted phenyl.

In certain embodiments, a compound of the present invention isrepresented by G and the attendant definitions, wherein R₅ represents H,alkyl, or aralkyl.

In certain embodiments, a compound of the present invention isrepresented by G and the attendant definitions, wherein m is 1.

In certain embodiments, a compound of the present invention isrepresented by G and the attendant definitions, wherein n is 1.

In certain embodiments, a compound of the present invention isrepresented by G and the attendant definitions, wherein X represents O;and Y represents O.

In certain embodiments, a compound of the present invention isrepresented by G and the attendant definitions, wherein X represents O;and R represents alkyl.

In certain embodiments, a compound of the present invention isrepresented by G and the attendant definitions, wherein X represents O;and R₃ represents optionally substituted phenyl.

In certain embodiments, a compound of the present invention isrepresented by G and the attendant definitions, wherein X represents O;and R₅ represents H, alkyl, or aralkyl.

In certain embodiments, a compound of the present invention isrepresented by G and the attendant definitions, wherein X represents O;and m is 1.

In certain embodiments, a compound of the present invention isrepresented by G and the attendant definitions, wherein X represents O;and n is 1.

In certain embodiments, a compound of the present invention isrepresented by G and the attendant definitions, wherein X represents O;Y represents O; R represents alkyl; and R₃ represents optionallysubstituted phenyl.

In certain embodiments, a compound of the present invention isrepresented by G and the attendant definitions, wherein X represents O;Y represents O; R represents alkyl; and R₅ represents H, alkyl, oraralkyl.

In certain embodiments, a compound of the present invention isrepresented by G and the attendant definitions, wherein X represents O;Y represents O; R represents alkyl; R₃ represents optionally substitutedphenyl; and R₅ represents H, alkyl, or aralkyl.

In certain embodiments, a compound of the present invention isrepresented by G and the attendant definitions, wherein X represents O;Y represents O; R represents methyl; R₃ represents 4-chlorophenyl; R₅represents ethyl; m is 1; and n is 1.

In certain embodiments, a compound of the present invention isrepresented by H:

wherein

-   -   X represents O or S;    -   Y represents O or S;    -   R represents H, alkyl, alkoxyl, alkylamino, aryl, heteroaryl,        aralkyl, heteroaralkyl, acyl, alkoxycarbonyl, or        alkylaminocarbonyl;    -   R₁ represents H;    -   R₃ represents H;    -   R₄ represents optionally substituted aryl or heteroaryl;    -   R₅ represents H, alkyl, alkoxyl, alkylamino, aryl, heteroaryl,        aralkyl, heteroaralkyl, acyl, alkoxycarbonyl, or        alkylaminocarbonyl;    -   m is 1 or 2; and    -   n is 0, 1, or 2.

In certain embodiments, a compound of the present invention isrepresented by H and the attendant definitions, wherein X represents O.

In certain embodiments, a compound of the present invention isrepresented by H and the attendant definitions, wherein Y represents O.

In certain embodiments, a compound of the present invention isrepresented by H and the attendant definitions, wherein R representsalkyl.

In certain embodiments, a compound of the present invention isrepresented by H and the attendant definitions, wherein R₄ representsoptionally substituted phenyl.

In certain embodiments, a compound of the present invention isrepresented by H and the attendant definitions, wherein R₅ represents H,alkyl, or aralkyl.

In certain embodiments, a compound of the present invention isrepresented by H and the attendant definitions, wherein m is 1.

In certain embodiments, a compound of the present invention isrepresented by H and the attendant definitions, wherein n is 1.

In certain embodiments, a compound of the present invention isrepresented by H and the attendant definitions, wherein X represents O;and Y represents O.

In certain embodiments, a compound of the present invention isrepresented by H and the attendant definitions, wherein X represents O;and R represents alkyl.

In certain embodiments, a compound of the present invention isrepresented by H and the attendant definitions, wherein X represents O;and R₄ represents optionally substituted phenyl.

In certain embodiments, a compound of the present invention isrepresented by H and the attendant definitions, wherein X represents O;and R₅ represents H, alkyl, or aralkyl.

In certain embodiments, a compound of the present invention isrepresented by H and the attendant definitions, wherein X represents O;and m is 1.

In certain embodiments, a compound of the present invention isrepresented by H and the attendant definitions, wherein X represents O;and n is 1.

In certain embodiments, a compound of the present invention isrepresented by H and the attendant definitions, wherein X represents O;Y represents O; R represents alkyl; and R₄ represents optionallysubstituted phenyl.

In certain embodiments, a compound of the present invention isrepresented by H and the attendant definitions, wherein X represents O;Y represents O; R represents alkyl; and R₅ represents H, alkyl, oraralkyl.

In certain embodiments, a compound of the present invention isrepresented by H and the attendant definitions, wherein X represents O;Y represents O; R represents alkyl; R₄ represents optionally substitutedphenyl; and R₅ represents H, alkyl, or aralkyl.

In certain embodiments, a compound of the present invention isrepresented by H and the attendant definitions, wherein X represents O;Y represents O; R represents methyl; R₄ represents 4-chlorophenyl; R₅represents ethyl; m is 1; and n is 1.

In certain embodiments, a compound of the present invention isrepresented by I:

wherein

-   -   X represents O or (H)₂;    -   R represents H, alkyl, alkoxyl, alkylamino, aryl, heteroaryl,        aralkyl, heteroaralkyl, acyl, alkoxycarbonyl, or        alkylaminocarbonyl;    -   R₁ represents —C(O)OR;    -   R₂ represents H;    -   R₃ represents optionally substituted aryl or heteroaryl;    -   R₄ represents H;    -   R₅ represents independently for each occurrence H, alkyl,        alkoxyl, alkylamino, aryl, heteroaryl, aralkyl, heteroaralkyl,        acyl, alkoxycarbonyl, or alkylaminocarbonyl; and    -   n is 1, 2, 3, 4, or 5.

In certain embodiments, a compound of the present invention isrepresented by I and the attendant definitions, wherein X represents O.

In certain embodiments, a compound of the present invention isrepresented by I and the attendant definitions, wherein R representsalkyl.

In certain embodiments, a compound of the present invention isrepresented by I and the attendant definitions, wherein R₃ representsoptionally substituted phenyl.

In certain embodiments, a compound of the present invention isrepresented by I and the attendant definitions, wherein R₅ represents Hor aralkyl.

In certain embodiments, a compound of the present invention isrepresented by I and the attendant definitions, wherein n is 3.

In certain embodiments, a compound of the present invention isrepresented by I and the attendant definitions, wherein X represents O;and R represents alkyl.

In certain embodiments, a compound of the present invention isrepresented by I and the attendant definitions, wherein X represents O;and R₃ represents optionally substituted phenyl.

In certain embodiments, a compound of the present invention isrepresented by I and the attendant definitions, wherein X represents O;and R₅ represents independently for each occurrence H or aralkyl.

In certain embodiments, a compound of the present invention isrepresented by I and the attendant definitions, wherein X represents O;and n is 3.

In certain embodiments, a compound of the present invention isrepresented by I and the attendant definitions, wherein X represents O;R represents alkyl; and R₃ represents optionally substituted phenyl.

In certain embodiments, a compound of the present invention isrepresented by I and the attendant definitions, wherein X represents O;R represents alkyl; and R₅ represents independently for each occurrenceH or aralkyl.

In certain embodiments, a compound of the present invention isrepresented by I and the attendant definitions, wherein X represents O;R represents alkyl; R₃ represents optionally substituted phenyl; and R₅represents independently for each occurrence H or aralkyl.

In certain embodiments, a compound of the present invention isrepresented by I and the attendant definitions, wherein X represents O;R represents methyl; R₃ represents 4-chlorophenyl; R₅ representsindependently for each occurrence H or triphenylmethyl; and n is 3.

In certain embodiments, a compound of the present invention isrepresented by J:

wherein

-   -   X represents O or S;    -   Y represents O or S;    -   R represents H, alkyl, alkoxyl, alkylamino, aryl, heteroaryl,        aralkyl, heteroaralkyl, acyl, alkoxycarbonyl, or        alkylaminocarbonyl;    -   R₁ represents —C(O)OR;    -   R₂ represents H;    -   R₃ represents optionally substituted aryl or heteroaryl;    -   R₄ represents H;    -   R₅ represents H, alkyl, alkoxyl, alkylamino, aryl, heteroaryl,        aralkyl, heteroaralkyl, acyl, alkoxycarbonyl, or        alkylaminocarbonyl;    -   m is 1 or 2; and    -   n is 0, 1, or 2.

In certain embodiments, a compound of the present invention isrepresented by J and the attendant definitions, wherein X represents O.

In certain embodiments, a compound of the present invention isrepresented by J and the attendant definitions, wherein Y represents O.

In certain embodiments, a compound of the present invention isrepresented by J and the attendant definitions, wherein R representsalkyl.

In certain embodiments, a compound of the present invention isrepresented by J and the attendant definitions, wherein R₃ representsoptionally substituted phenyl.

In certain embodiments, a compound of the present invention isrepresented by J and the attendant definitions, wherein R₅ represents H,alkyl, or aralkyl.

In certain embodiments, a compound of the present invention isrepresented by J and the attendant definitions, wherein m is 1.

In certain embodiments, a compound of the present invention isrepresented by J and the attendant definitions, wherein X represents O;and Y represents O.

In certain embodiments, a compound of the present invention isrepresented by J and the attendant definitions, wherein X represents O;and R represents alkyl.

In certain embodiments, a compound of the present invention isrepresented by J and the attendant definitions, wherein X represents O;and R₃ represents optionally substituted phenyl.

In certain embodiments, a compound of the present invention isrepresented by J and the attendant definitions, wherein X represents O;and R₅ represents H, alkyl, or aralkyl.

In certain embodiments, a compound of the present invention isrepresented by J and the attendant definitions, wherein X represents O;and m is 1.

In certain embodiments, a compound of the present invention isrepresented by J and the attendant definitions, wherein X represents O;Y represents O; R represents alkyl; and R₃ represents optionallysubstituted phenyl.

In certain embodiments, a compound of the present invention isrepresented by J and the attendant definitions, wherein X represents O;Y represents O; R represents alkyl; and R₅ represents H, alkyl, oraralkyl.

In certain embodiments, a compound of the present invention isrepresented by J and the attendant definitions, wherein X represents O;Y represents O; R represents alkyl; R₃ represents optionally substitutedphenyl; and R₅ represents H, alkyl, or aralkyl.

In certain embodiments, a compound of the present invention isrepresented by J and the attendant definitions, wherein X represents O;Y represents O; R represents methyl; R₃ represents 4-chlorophenyl; R₅represents ethyl; and m is 1.

In certain embodiments, the present invention relates to a complexcomprising a radionuclide and a compound represented by A, B, C, D, E,F, G, H, I, or J. In certain embodiments of this method, theradionuclide is technetium.

In certain embodiments, the present invention relates to methods ofimaging brain tissue of a mammal, comprising the step of administeringto a mammal a sufficient amount of a complex comprising a radionuclideand a compound represented by A, B, C, D, E, F, G, H, I, or J. Incertain embodiments of this method, the radionuclide is technetium.

In certain embodiments, the present invention relates to methods ofimaging dopamine transporters in brain tissue of a mammal, comprisingthe step of administering to a mammal a sufficient amount of a complexcomprising a radionuclide and a compound represented by A, B, C, D, E,F, G, H, I, or J. In certain embodiments of this method, theradionuclide is technetium.

Pharmaceutical Compositions

In another aspect, the present invention provides pharmaceuticallyacceptable compositions which comprise a therapeutically-effectiveamount of one or more of the compounds described above, formulatedtogether with one or more pharmaceutically acceptable carriers(additives) and/or diluents. As described in detail below, thepharmaceutical compositions of the present invention may be speciallyformulated for administration in solid or liquid form, including thoseadapted for the following: (1) oral administration, for example,drenches (aqueous or non-aqueous solutions or suspensions), tablets,e.g., those targeted for buccal, sublingual, and systemic absorption,boluses, powders, granules, pastes for application to the tongue; (2)parenteral administration, for example, by subcutaneous, intramuscular,intravenous or epidural injection as, for example, a sterile solution orsuspension, or sustained-release formulation; (3) topical application,for example, as a cream, ointment, or a controlled-release patch orspray applied to the skin; (4) intravaginally or intrarectally, forexample, as a pessary, cream or foam; (5) sublingually; (6) ocularly;(7) transdermally; or (8) nasally.

The phrase “therapeutically-effective amount” as used herein means thatamount of a compound, material, or composition comprising a compound ofthe present invention which is effective for producing some desiredtherapeutic effect in at least a sub-population of cells in an animal ata reasonable benefit/risk ratio applicable to any medical treatment.

The phrase “pharmaceutically acceptable” is employed herein to refer tothose compounds, materials, compositions, and/or dosage forms which are,within the scope of sound medical judgment, suitable for use in contactwith the tissues of human beings and animals without excessive toxicity,irritation, allergic response, or other problem or complication,commensurate with a reasonable benefit/risk ratio.

The phrase “pharmaceutically-acceptable carrier” as used herein means apharmaceutically-acceptable material, composition or vehicle, such as aliquid or solid filler, diluent, excipient, or solvent encapsulatingmaterial, involved in carrying or transporting the subject compound fromone organ, or portion of the body, to another organ, or portion of thebody. Each carrier must be “acceptable” in the sense of being compatiblewith the other ingredients of the formulation and not injurious to thepatient. Some examples of materials which can serve aspharmaceutically-acceptable carriers include: (1) sugars, such aslactose, glucose and sucrose; (2) starches, such as corn starch andpotato starch; (3) cellulose, and its derivatives, such as sodiumcarboxymethyl cellulose, ethyl cellulose and cellulose acetate; (4)powdered tragacanth; (5) malt; (6) gelatin; (7) talc; (8) excipients,such as cocoa butter and suppository waxes; (9) oils, such as peanutoil, cottonseed oil, safflower oil, sesame oil, olive oil, corn oil andsoybean oil; (10) glycols, such as propylene glycol; (11) polyols, suchas glycerin, sorbitol, mannitol and polyethylene glycol; (12) esters,such as ethyl oleate and ethyl laurate; (13) agar; (14) bufferingagents, such as magnesium hydroxide and aluminum hydroxide; (15) alginicacid; (16) pyrogen-free water; (17) isotonic saline; (18) Ringer'ssolution; (19) ethyl alcohol; (20) pH buffered solutions; (21)polyesters, polycarbonates and/or polyanhydrides; and (22) othernon-toxic compatible substances employed in pharmaceutical formulations.

As set out above, certain embodiments of the present compounds maycontain a basic functional group, such as amino or alkylamino, and are,thus, capable of forming pharmaceutically-acceptable salts withpharmaceutically-acceptable acids. The term “pharmaceutically-acceptablesalts” in this respect, refers to the relatively non-toxic, inorganicand organic acid addition salts of compounds of the present invention.These salts can be prepared in situ in the administration vehicle or thedosage form manufacturing process, or by separately reacting a purifiedcompound of the invention in its free base form with a suitable organicor inorganic acid, and isolating the salt thus formed during subsequentpurification. Representative salts include the hydrobromide,hydrochloride, sulfate, bisulfate, phosphate, nitrate, acetate,valerate, oleate, palmitate, stearate, laurate, benzoate, lactate,phosphate, tosylate, citrate, maleate, fumarate, succinate, tartrate,napthylate, mesylate, glucoheptonate, lactobionate, and laurylsulphonatesalts and the like. (See, for example, Berge et al. (1977)“Pharmaceutical Salts”, J. Pharm. Sci. 66:1-19)

The pharmaceutically acceptable salts of the subject compounds includethe conventional nontoxic salts or quaternary ammonium salts of thecompounds, e.g., from non-toxic organic or inorganic acids. For example,such conventional nontoxic salts include those derived from inorganicacids such as hydrochloride, hydrobromic, sulfuric, sulfamic,phosphoric, nitric, and the like; and the salts prepared from organicacids such as acetic, propionic, succinic, glycolic, stearic, lactic,malic, tartaric, citric, ascorbic, palmitic, maleic, hydroxymaleic,phenylacetic, glutamic, benzoic, salicyclic, sulfanilic,2-acetoxybenzoic, fumaric, toluenesulfonic, methanesulfonic, ethanedisulfonic, oxalic, isothionic, and the like.

In other cases, the compounds of the present invention may contain oneor more acidic functional groups and, thus, are capable of formingpharmaceutically-acceptable salts with pharmaceutically-acceptablebases. The term “pharmaceutically-acceptable salts” in these instancesrefers to the relatively non-toxic, inorganic and organic base additionsalts of compounds of the present invention. These salts can likewise beprepared in situ in the administration vehicle or the dosage formmanufacturing process, or by separately reacting the purified compoundin its free acid form with a suitable base, such as the hydroxide,carbonate or bicarbonate of a pharmaceutically-acceptable metal cation,with ammonia, or with a pharmaceutically-acceptable organic primary,secondary or tertiary amine. Representative alkali or alkaline earthsalts include the lithium, sodium, potassium, calcium, magnesium, andaluminum salts and the like. Representative organic amines useful forthe formation of base addition salts include ethylamine, diethylamine,ethylenediamine, ethanolamine, diethanolamine, piperazine and the like.(See, for example, Berge et al., supra)

Wetting agents, emulsifiers and lubricants, such as sodium laurylsulfate and magnesium stearate, as well as coloring agents, releaseagents, coating agents, sweetening, flavoring and perfuming agents,preservatives and antioxidants can also be present in the compositions.

Examples of pharmaceutically-acceptable antioxidants include: (1) watersoluble antioxidants, such as ascorbic acid, cysteine hydrochloride,sodium bisulfate, sodium metabisulfite, sodium sulfite and the like; (2)oil-soluble antioxidants, such as ascorbyl palmitate, butylatedhydroxyanisole (BHA), butylated hydroxytoluene (BHT), lecithin, propylgallate, alpha-tocopherol, and the like; and (3) metal chelating agents,such as citric acid, ethylenediamine tetraacetic acid (EDTA), sorbitol,tartaric acid, phosphoric acid, and the like.

Formulations of the present invention include those suitable for oral,nasal, topical (including buccal and sublingual), rectal, vaginal and/orparenteral administration. The formulations may conveniently bepresented in unit dosage form and may be prepared by any methods wellknown in the art of pharmacy. The amount of active ingredient which canbe combined with a carrier material to produce a single dosage form willvary depending upon the host being treated, the particular mode ofadministration. The amount of active ingredient which can be combinedwith a carrier material to produce a single dosage form will generallybe that amount of the compound which produces a therapeutic effect.Generally, out of one hundred per cent, this amount will range fromabout 1 per cent to about ninety-nine percent of active ingredient,preferably from about 5 per cent to about 70 per cent, most preferablyfrom about 10 per cent to about 30 per cent.

In certain embodiments, a formulation of the present invention comprisesan excipient selected from the group consisting of cyclodextrins,liposomes, micelle forming agents, e.g., bile acids, and polymericcarriers, e.g., polyesters and polyanhydrides; and a compound of thepresent invention. In certain embodiments, an aforementioned formulationrenders orally bioavailable a compound of the present invention.

Methods of preparing these formulations or compositions include the stepof bringing into association a compound of the present invention withthe carrier and, optionally, one or more accessory ingredients. Ingeneral, the formulations are prepared by uniformly and intimatelybringing into association a compound of the present invention withliquid carriers, or finely divided solid carriers, or both, and then, ifnecessary, shaping the product.

Formulations of the invention suitable for oral administration may be inthe form of capsules, cachets, pills, tablets, lozenges (using aflavored basis, usually sucrose and acacia or tragacanth), powders,granules, or as a solution or a suspension in an aqueous or non-aqueousliquid, or as an oil-in-water or water-in-oil liquid emulsion, or as anelixir or syrup, or as pastilles (using an inert base, such as gelatinand glycerin, or sucrose and acacia) and/or as mouth washes and thelike, each containing a predetermined amount of a compound of thepresent invention as an active ingredient. A compound of the presentinvention may also be administered as a bolus, electuary or paste.

In solid dosage forms of the invention for oral administration(capsules, tablets, pills, dragees, powders, granules and the like), theactive ingredient is mixed with one or more pharmaceutically-acceptablecarriers, such as sodium citrate or dicalcium phosphate, and/or any ofthe following: (1) fillers or extenders, such as starches, lactose,sucrose, glucose, mannitol, and/or silicic acid; (2) binders, such as,for example, carboxymethylcellulose, alginates, gelatin, polyvinylpyrrolidone, sucrose and/or acacia; (3) humectants, such as glycerol;(4) disintegrating agents, such as agar-agar, calcium carbonate, potatoor tapioca starch, alginic acid, certain silicates, and sodiumcarbonate; (5) solution retarding agents, such as paraffin; (6)absorption accelerators, such as quaternary ammonium compounds; (7)wetting agents, such as, for example, cetyl alcohol, glycerolmonostearate, and non-ionic surfactants; (8) absorbents, such as kaolinand bentonite clay; (9) lubricants, such a talc, calcium stearate,magnesium stearate, solid polyethylene glycols, sodium lauryl sulfate,and mixtures thereof; and (10) coloring agents. In the case of capsules,tablets and pills, the pharmaceutical compositions may also comprisebuffering agents. Solid compositions of a similar type may also beemployed as fillers in soft and hard-shelled gelatin capsules using suchexcipients as lactose or milk sugars, as well as high molecular weightpolyethylene glycols and the like.

A tablet may be made by compression or molding, optionally with one ormore accessory ingredients. Compressed tablets may be prepared usingbinder (for example, gelatin or hydroxypropylmethyl cellulose),lubricant, inert diluent, preservative, disintegrant (for example,sodium starch glycolate or cross-linked sodium carboxymethyl cellulose),surface-active or dispersing agent. Molded tablets may be made bymolding in a suitable machine a mixture of the powdered compoundmoistened with an inert liquid diluent.

The tablets, and other solid dosage forms of the pharmaceuticalcompositions of the present invention, such as dragees, capsules, pillsand granules, may optionally be scored or prepared with coatings andshells, such as enteric coatings and other coatings well known in thepharmaceutical-formulating art. They may also be formulated so as toprovide slow or controlled release of the active ingredient thereinusing, for example, hydroxypropylmethyl cellulose in varying proportionsto provide the desired release profile, other polymer matrices,liposomes and/or microspheres. They may be formulated for rapid release,e.g., freeze-dried. They may be sterilized by, for example, filtrationthrough a bacteria-retaining filter, or by incorporating sterilizingagents in the form of sterile solid compositions which can be dissolvedin sterile water, or some other sterile injectable medium immediatelybefore use. These compositions may also optionally contain opacifyingagents and may be of a composition that they release the activeingredient(s) only, or preferentially, in a certain portion of thegastrointestinal tract, optionally, in a delayed manner. Examples ofembedding compositions which can be used include polymeric substancesand waxes. The active ingredient can also be in micro-encapsulated form,if appropriate, with one or more of the above-described excipients.

Liquid dosage forms for oral administration of the compounds of theinvention include pharmaceutically acceptable emulsions, microemulsions,solutions, suspensions, syrups and elixirs. In addition to the activeingredient, the liquid dosage forms may contain inert diluents commonlyused in the art, such as, for example, water or other solvents,solubilizing agents and emulsifiers, such as ethyl alcohol, isopropylalcohol, ethyl carbonate, ethyl acetate, benzyl alcohol, benzylbenzoate, propylene glycol, 1,3-butylene glycol, oils (in particular,cottonseed, groundnut, corn, germ, olive, castor and sesame oils),glycerol, tetrahydrofuryl alcohol, polyethylene glycols and fatty acidesters of sorbitan, and mixtures thereof.

Besides inert diluents, the oral compositions can also include adjuvantssuch as wetting agents, emulsifying and suspending agents, sweetening,flavoring, coloring, perfuming and preservative agents.

Suspensions, in addition to the active compounds, may contain suspendingagents as, for example, ethoxylated isostearyl alcohols, polyoxyethylenesorbitol and sorbitan esters, microcrystalline cellulose, aluminummetahydroxide, bentonite, agar-agar and tragacanth, and mixturesthereof.

Formulations of the pharmaceutical compositions of the invention forrectal or vaginal administration may be presented as a suppository,which may be prepared by mixing one or more compounds of the inventionwith one or more suitable nonirritating excipients or carrierscomprising, for example, cocoa butter, polyethylene glycol, asuppository wax or a salicylate, and which is solid at room temperature,but liquid at body temperature and, therefore, will melt in the rectumor vaginal cavity and release the active compound.

Formulations of the present invention which are suitable for vaginaladministration also include pessaries, tampons, creams, gels, pastes,foams or spray formulations containing such carriers as are known in theart to be appropriate.

Dosage forms for the topical or transdermal administration of a compoundof this invention include powders, sprays, ointments, pastes, creams,lotions, gels, solutions, patches and inhalants. The active compound maybe mixed under sterile conditions with a pharmaceutically-acceptablecarrier, and with any preservatives, buffers, or propellants which maybe required.

The ointments, pastes, creams and gels may contain, in addition to anactive compound of this invention, excipients, such as animal andvegetable fats, oils, waxes, paraffins, starch, tragacanth, cellulosederivatives, polyethylene glycols, silicones, bentonites, silicic acid,talc and zinc oxide, or mixtures thereof.

Powders and sprays can contain, in addition to a compound of thisinvention, excipients such as lactose, talc, silicic acid, aluminumhydroxide, calcium silicates and polyamide powder, or mixtures of thesesubstances. Sprays can additionally contain customary propellants, suchas chlorofluorohydrocarbons and volatile unsubstituted hydrocarbons,such as butane and propane.

Transdermal patches have the added advantage of providing controlleddelivery of a compound of the present invention to the body. Such dosageforms can be made by dissolving or dispersing the compound in the propermedium. Absorption enhancers can also be used to increase the flux ofthe compound across the skin. The rate of such flux can be controlled byeither providing a rate controlling membrane or dispersing the compoundin a polymer matrix or gel.

Ophthalmic formulations, eye ointments, powders, solutions and the like,are also contemplated as being within the scope of this invention.

Pharmaceutical compositions of this invention suitable for parenteraladministration comprise one or more compounds of the invention incombination with one or more pharmaceutically-acceptable sterileisotonic aqueous or nonaqueous solutions, dispersions, suspensions oremulsions, or sterile powders which may be reconstituted into sterileinjectable solutions or dispersions just prior to use, which may containsugars, alcohols, antioxidants, buffers, bacteriostats, solutes whichrender the formulation isotonic with the blood of the intended recipientor suspending or thickening agents.

Examples of suitable aqueous and nonaqueous carriers which may beemployed in the pharmaceutical compositions of the invention includewater, ethanol, polyols (such as glycerol, propylene glycol,polyethylene glycol, and the like), and suitable mixtures thereof,vegetable oils, such as olive oil, and injectable organic esters, suchas ethyl oleate. Proper fluidity can be maintained, for example, by theuse of coating materials, such as lecithin, by the maintenance of therequired particle size in the case of dispersions, and by the use ofsurfactants.

These compositions may also contain adjuvants such as preservatives,wetting agents, emulsifying agents and dispersing agents. Prevention ofthe action of microorganisms upon the subject compounds may be ensuredby the inclusion of various antibacterial and antifungal agents, forexample, paraben, chlorobutanol, phenol sorbic acid, and the like. Itmay also be desirable to include isotonic agents, such as sugars, sodiumchloride, and the like into the compositions. In addition, prolongedabsorption of the injectable pharmaceutical form may be brought about bythe inclusion of agents which delay absorption such as aluminummonostearate and gelatin.

In some cases, in order to prolong the effect of a drug, it is desirableto slow the absorption of the drug from subcutaneous or intramuscularinjection. This may be accomplished by the use of a liquid suspension ofcrystalline or amorphous material having poor water solubility. The rateof absorption of the drug then depends upon its rate of dissolutionwhich, in turn, may depend upon crystal size and crystalline form.Alternatively, delayed absorption of a parenterally-administered drugform is accomplished by dissolving or suspending the drug in an oilvehicle.

Injectable depot forms are made by forming microencapsule matrices ofthe subject compounds in biodegradable polymers such aspolylactide-polyglycolide. Depending on the ratio of drug to polymer,and the nature of the particular polymer employed, the rate of drugrelease can be controlled. Examples of other biodegradable polymersinclude poly(orthoesters) and poly(anhydrides). Depot injectableformulations are also prepared by entrapping the drug in liposomes ormicroemulsions which are compatible with body tissue.

When the compounds of the present invention are administered aspharmaceuticals, to humans and animals, they can be given per se or as apharmaceutical composition containing, for example, 0.1 to 99.5% (morepreferably, 0.5 to 90%) of active ingredient in combination with apharmaceutically acceptable carrier.

The preparations of the present invention may be given orally,parenterally, topically, or rectally. They are of course given in formssuitable for each administration route. For example, they areadministered in tablets or capsule form, by injection, inhalation, eyelotion, ointment, suppository, etc. administration by injection,infusion or inhalation; topical by lotion or ointment; and rectal bysuppositories. Oral administrations are preferred.

The phrases “parenteral administration” and “administered parenterally”as used herein means modes of administration other than enteral andtopical administration, usually by injection, and includes, withoutlimitation, intravenous, intramuscular, intraarterial, intrathecal,intracapsular, intraorbital, intracardiac, intradermal, intraperitoneal,transtracheal, subcutaneous, subcuticular, intraarticulare, subcapsular,subarachnoid, intraspinal and intrasternal injection and infusion.

The phrases “systemic administration,” “administered systemically,”“peripheral administration” and “administered peripherally” as usedherein mean the administration of a compound, drug or other materialother than directly into the central nervous system, such that it entersthe patient's system and, thus, is subject to metabolism and other likeprocesses, for example, subcutaneous administration.

These compounds may be administered to humans and other animals fortherapy by any suitable route of administration, including orally,nasally, as by, for example, a spray, rectally, intravaginally,parenterally, intracistemally and topically, as by powders, ointments ordrops, including buccally and sublingually.

Regardless of the route of administration selected, the compounds of thepresent invention, which may be used in a suitable hydrated form, and/orthe pharmaceutical compositions of the present invention, are formulatedinto pharmaceutically-acceptable dosage forms by conventional methodsknown to those of skill in the art.

Actual dosage levels of the active ingredients in the pharmaceuticalcompositions of this invention may be varied so as to obtain an amountof the active ingredient which is effective to achieve the desiredtherapeutic response for a particular patient, composition, and mode ofadministration, without being toxic to the patient.

The selected dosage level will depend upon a variety of factorsincluding the activity of the particular compound of the presentinvention employed, or the ester, salt or amide thereof, the route ofadministration, the time of administration, the rate of excretion ormetabolism of the particular compound being employed, the duration ofthe treatment, other drugs, compounds and/or materials used incombination with the particular compound employed, the age, sex, weight,condition, general health and prior medical history of the patient beingtreated, and like factors well known in the medical arts.

A physician or veterinarian having ordinary skill in the art can readilydetermine and prescribe the effective amount of the pharmaceuticalcomposition required. For example, the physician or veterinarian couldstart doses of the compounds of the invention employed in thepharmaceutical composition at levels lower than that required in orderto achieve the desired therapeutic effect and gradually increase thedosage until the desired effect is achieved.

In general, a suitable daily dose of a compound of the invention will bethat amount of the compound which is the lowest dose effective toproduce a therapeutic effect. Such an effective dose will generallydepend upon the factors described above. Generally, intravenous,intracerebroventricular and subcutaneous doses of the compounds of thisinvention for a patient, when used for the indicated analgesic effects,will range from about 0.0001 to about 100 mg per kilogram of body weightper day.

If desired, the effective daily dose of the active compound may beadministered as two, three, four, five, six or more sub-dosesadministered separately at appropriate intervals throughout the day,optionally, in unit dosage forms.

While it is possible for a compound of the present invention to beadministered alone, it is preferable to administer the compound as apharmaceutical formulation (composition).

In another aspect, the present invention provides pharmaceuticallyacceptable compositions which comprise a therapeutically-effectiveamount of one or more of the subject compounds, as described above,formulated together with one or more pharmaceutically acceptablecarriers (additives) and/or diluents. As described in detail below, thepharmaceutical compositions of the present invention may be speciallyformulated for administration in solid or liquid form, including thoseadapted for the following: (1) oral administration, for example,drenches (aqueous or non-aqueous solutions or suspensions), tablets,boluses, powders, granules, pastes for application to the tongue; (2)parenteral administration, for example, by subcutaneous, intramuscularor intravenous injection as, for example, a sterile solution orsuspension; (3) topical application, for example, as a cream, ointmentor spray applied to the skin, lungs, or oral cavity; or (4)intravaginally or intravectally, for example, as a pessary, cream orfoam; (5) sublingually; (6) ocularly; (7) transdermally; or (8) nasally.

The compounds according to the invention may be formulated foradministration in any convenient way for use in human or veterinarymedicine, by analogy with other pharmaceuticals.

The term “treatment” is intended to encompass also prophylaxis, therapyand cure.

The patient receiving this treatment is any animal in need, includingprimates, in particular humans, and other mammals such as equines,cattle, swine and sheep; and poultry and pets in general.

The compounds of the invention can be administered as such or inadmixtures with pharmaceutically acceptable carriers and can also beadministered in conjunction with antimicrobial agents such aspenicillins, cephalosporins, aminoglycosides and glycopeptides.Conjunctive therapy, thus includes sequential, simultaneous and separateadministration of the active compound in a way that the therapeuticaleffects of the first administered one is not entirely disappeared whenthe subsequent is administered.

The addition of the active compound of the invention to animal feed ispreferably accomplished b y preparing an appropriate feed premixcontaining the active compound in an effective amount and incorporatingthe premix into the complete ration.

Alternatively, an intermediate concentrate or feed supplement containingthe active ingredient can be blended into the feed. The way in whichsuch feed premixes and complete rations can be prepared and administeredare described in reference books (such as “Applied Animal Nutrition”, W.H. Freedman and CO., San Francisco, U.S.A., 1969 or “Livestock Feeds andFeeding” O and B books, Corvallis, Oreg., U.S.A., 1977).

Combinatorial Libraries

Combinatorial libraries of the compounds of the present invention may beprepared for the screening of pharmaceutical, agrochemical or otherbiological or medically-related activity or material-related qualities.A combinatorial library for the purposes of the present invention is amixture of chemically related compounds which may be screened togetherfor a desired property; said libraries may be in solution or covalentlylinked to a solid support. The preparation of many related compounds ina single reaction greatly reduces and simplifies the number of screeningprocesses which need to be carried out. Screening for the appropriatebiological, pharmaceutical, agrochemical or physical property may bedone by conventional methods.

Diversity in a library can be created at a variety of different levels.For instance, the substrate aryl groups used in a combinatorial approachcan be diverse in terms of the core aryl moiety, e.g., a variegation interms of the ring structure, and/or can be varied with respect to theother substituents.

A variety of techniques are available in the art for generatingcombinatorial libraries of small organic molecules. See, for example,Blondelle et al. (1995) Trends Anal. Chem. 14:83; the Affymax U.S. Pat.Nos. 5,359,115 and 5,362,899: the Ellman U.S. Pat. No. 5,288,514: theStill et al. PCT publication WO 94/08051; Chen et al. (1994) JACS116:2661: Kerr et al. (1993) JACS 115:252; PCT publications WO92/10092,WO93/09668 and WO91/07087; and the Lerner et al. PCT publicationWO93/20242). Accordingly, a variety of libraries on the order of about16 to 1,000,000 or more diversomers can be synthesized and screened fora particular activity or property.

In an exemplary embodiment, a library of substituted diversomers can besynthesized using the subject reactions adapted to the techniquesdescribed in the Still et al. PCT publication WO 94/0805 1, e.g., beinglinked to a polymer bead by a hydrolyzable or photolyzable group, e.g.,located at one of the positions of substrate. According to the Still etal. technique, the library is synthesized on a set of beads, each beadincluding a set of tags identifying the particular diversomer on thatbead. In one embodiment, which is particularly suitable for discoveringenzyme inhibitors, the beads can be dispersed on the surface of apermeable membrane, and the diversomers released from the beads by lysisof the bead linker. The diversomer from each bead will diffuse acrossthe membrane to an assay zone, where it will interact with an enzymeassay. Detailed descriptions of a number of combinatorial methodologiesare provided below.

A) Direct Characterization

A growing trend in the field of combinatorial chemistry is to exploitthe sensitivity of techniques such as mass spectrometry (MS), e.g.,which can be used to characterize sub-femtomolar amounts of a compound,and to directly determine the chemical constitution of a compoundselected from a combinatorial library. For instance, where the libraryis provided on an insoluble support matrix, discrete populations ofcompounds can be first released from the support and characterized byMS. In other embodiments, as part of the MS sample preparationtechnique, such MS techniques as MALDI can be used to release a compoundfrom the matrix, particularly where a labile bond is used originally totether the compound to the matrix. For instance, a bead selected from alibrary can be irradiated in a MALDI step in order to release thediversomer from the matrix, and ionize the diversomer for MS analysis.

B) Multipin Synthesis

The libraries of the subject method can take the multipin libraryformat. Briefly, Geysen and co-workers (Geysen et al. (1984) PNAS81:3998-4002) introduced a method for generating compound libraries by aparallel synthesis on polyacrylic acid-grated polyethylene pins arrayedin the microtitre plate format. The Geysen technique can be used tosynthesize and screen thousands of compounds per week using the multipinmethod, and the tethered compounds may be reused in many assays.Appropriate linker moieties can also been appended to the pins so thatthe compounds may be cleaved from the supports after synthesis forassessment of purity and further evaluation (c.f., Bray et al. (1990)Tetrahedron Lett 31:5811-5814; Valerio et al. (1991) Anal Biochem197:168-177; Bray et al. (1991) Tetrahedron Lett 32:6163-6166).

C) Divide-Couple-Recombine

In yet another embodiment, a variegated library of compounds can beprovided on a set of beads utilizing the strategy ofdivide-couple-recombine (see, e.g., Houghten (1985) PNAS 82:5131-5135;and U.S. Pat. Nos. 4,631,211; 5,440,016; 5,480,971). Briefly, as thename implies, at each synthesis step where degeneracy is introduced intothe library, the beads are divided into separate groups equal to thenumber of different substituents to be added at a particular position inthe library, the different substituents coupled in separate reactions,and the beads recombined into one pool for the next iteration.

In one embodiment, the divide-couple-recombine strategy can be carriedout using an analogous approach to the so-called “tea bag” method firstdeveloped by Houghten, where compound synthesis occurs on resin sealedinside porous polypropylene bags (Houghten et al. (1986) PNAS82:5131-5135). Substituents are coupled to the compound-bearing resinsby placing the bags in appropriate reaction solutions, while all commonsteps such as resin washing and deprotection are performedsimultaneously in one reaction vessel. At the end of the synthesis, eachbag contains a single compound.

D) Combinatorial Libraries by Light-Directed, Spatially AddressableParallel Chemical Synthesis

A scheme of combinatorial synthesis in which the identity of a compoundis given by its locations on a synthesis substrate is termed aspatially-addressable synthesis. In one embodiment, the combinatorialprocess is carried out by controlling the addition of a chemical reagentto specific locations on a solid support (Dower et al. (1991) Annu RepMed Chem 26:271-280; Fodor, S.P.A. (1991) Science 251:767; Pirrung etal. (1992) U.S. Pat. No. 5,143,854; Jacobs et al. (1994) TrendsBiotechnol 12:19-26). The spatial resolution of photolithography affordsminiaturization. This technique can be carried out through the useprotection/deprotection reactions with photolabile protecting groups.

The key points of this technology are illustrated in Gallop et al.(1994) J Med Chem 37:1233-1251. A synthesis substrate is prepared forcoupling through the covalent attachment of photolabilenitroveratryloxycarbonyl (NVOC) protected amino linkers or otherphotolabile linkers. Light is used to selectively activate a specifiedregion of the synthesis support for coupling. Removal of the photolabileprotecting groups by light (deprotection) results in activation ofselected areas. After activation, the first of a set of amino acidanalogs, each bearing a photolabile protecting group on the aminoterminus, is exposed to the entire surface. Coupling only occurs inregions that were addressed by light in the preceding step. The reactionis stopped, the plates washed, and the substrate is again illuminatedthrough a second mask, activating a different region for reaction with asecond protected building block. The pattern of masks and the sequenceof reactants define the products and their locations. Since this processutilizes photolithography techniques, the number of compounds that canbe synthesized is limited only by the number of synthesis sites that canbe addressed with appropriate resolution. The position of each compoundis precisely known; hence, its interactions with other molecules can bedirectly assessed.

In a light-directed chemical synthesis, the products depend on thepattern of illumination and on the order of addition of reactants. Byvarying the lithographic patterns, many different sets of test compoundscan be synthesized simultaneously; this characteristic leads to thegeneration of many different masking strategies.

E) Encoded Combinatorial Libraries

In yet another embodiment, the subject method utilizes a compoundlibrary provided with an encoded tagging system. A recent improvement inthe identification of active compounds from combinatorial librariesemploys chemical indexing systems using tags that uniquely encode thereaction steps a given bead has undergone and, by inference, thestructure it carries. Conceptually, this approach mimics phage displaylibraries, where activity derives from expressed peptides, but thestructures of the active peptides are deduced from the correspondinggenomic DNA sequence. The first encoding of synthetic combinatoriallibraries employed DNA as the code. A variety of other forms of encodinghave been reported, including encoding with sequenceable bio-oligomers(e.g., oligonucleotides and peptides), and binary encoding withadditional non-sequenceable tags.

1) Tagging With Sequenceable Bio-Oligomers

The principle of using oligonucleotides to encode combinatorialsynthetic libraries was described in 1992 (Brenner et al. (1992) PNAS89:5381-5383), and an example of such a library appeared the followingyear (Needles et al. (1993) PNAS 90:10700-10704). A combinatoriallibrary of nominally 7⁷ (=823,543) peptides composed of all combinationsof Arg, Gln, Phe, Lys, Val, D-Val and Thr (three-letter amino acidcode), each of which was encoded by a specific dinucleotide (TA, TC, CT,AT, TT, CA and AC, respectively), was prepared by a series ofalternating rounds of peptide and oligonucleotide synthesis on solidsupport. In this work, the amine linking functionality on the bead wasspecifically differentiated toward peptide or oligonucleotide synthesisby simultaneously preincubating the beads with reagents that generateprotected OH groups for oligonucleotide synthesis and protected NH₂groups for peptide synthesis (here, in a ratio of 1:20). When complete,the tags each consisted of 69-mers, 14 units of which carried the code.The bead-bound library was incubated with a fluorescently labeledantibody, and beads containing bound antibody that fluoresced stronglywere harvested by fluorescence-activated cell sorting (FACS). The DNAtags were amplified by PCR and sequenced, and the predicted peptideswere synthesized. Following such techniques, compound libraries can bederived for use in the subject method, where the oligonucleotidesequence of the tag identifies the sequential combinatorial reactionsthat a particular bead underwent, and therefore provides the identity ofthe compound on the bead.

The use of oligonucleotide tags permits exquisitely sensitive taganalysis. Even so, the method requires careful choice of orthogonal setsof protecting groups required for alternating co-synthesis of the tagand the library member. Furthermore, the chemical lability of the tag,particularly the phosphate and sugar anomeric linkages, may limit thechoice of reagents and conditions that can be employed for the synthesisof non-oligomeric libraries. In preferred embodiments, the librariesemploy linkers permitting selective detachment of the test compoundlibrary member for assay.

Peptides have also been employed as tagging molecules for combinatoriallibraries. Two exemplary approaches are described in the art, both ofwhich employ branched linkers to solid phase upon which coding andligand strands are alternately elaborated. In the first approach (Kerr JM et al. (1993) J Am Chem Soc 115:2529-2531), orthogonality in synthesisis achieved by employing acid-labile protection for the coding strandand base-labile protection for the compound strand.

In an alternative approach (Nikolaiev et al. (1993) Pept Res 6:161-170),branched linkers are employed so that the coding unit and the testcompound can both be attached to the same functional group on the resin.In one embodiment, a cleavable linker can be placed between the branchpoint and the bead so that cleavage releases a molecule containing bothcode and the compound (Ptek et al. (1991) Tetrahedron Lett32:3891-3894). In another embodiment, the cleavable linker can be placedso that the test compound can be selectively separated from the bead,leaving the code behind. This last construct is particularly valuablebecause it permits screening of the test compound without potentialinterference of the coding groups. Examples in the art of independentcleavage and sequencing of peptide library members and theircorresponding tags has confirmed that the tags can accurately predictthe peptide structure.

2) Non-sequenceable Tagging: Binary Encoding

An alternative form of encoding the test compound library employs a setof non-sequencable electrophoric tagging molecules that are used as abinary code (Ohlmeyer et al. (1993) PNAS 90:10922-10926). Exemplary tagsare haloaromatic alkyl ethers that are detectable as theirtrimethylsilyl ethers at less than femtomolar levels by electron capturegas chromatography (ECGC). Variations in the length of the alkyl chain,as well as the nature and position of the aromatic halide substituents,permit the synthesis of at least 40 such tags, which in principle canencode 2⁴⁰ (e.g., upwards of 10¹²) different molecules. In the originalreport (Ohlmeyer et al., supra) the tags were bound to about 1% of theavailable amine groups of a peptide library via a photocleavableo-nitrobenzyl linker. This approach is convenient when preparingcombinatorial libraries of peptide-like or other amine-containingmolecules. A more versatile system has, however, been developed thatpermits encoding of essentially any combinatorial library. Here, thecompound would be attached to the solid support via the photocleavablelinker and the tag is attached through a catechol ether linker viacarbene insertion into the bead matrix (Nestler et al. (1994) J Org Chem59:4723-4724). This orthogonal attachment strategy permits the selectivedetachment of library members for assay in solution and subsequentdecoding by ECGC after oxidative detachment of the tag sets.

Although several amide-linked libraries in the art employ binaryencoding with the electrophoric tags attached to amine groups, attachingthese tags directly to the bead matrix provides far greater versatilityin the structures that can be prepared in encoded combinatoriallibraries. Attached in this way, the tags and their linker are nearly asunreactive as the bead matrix itself. Two binary-encoded combinatoriallibraries have been reported where the electrophoric tags are attacheddirectly to the solid phase (Ohlmeyer et al. (1995) PNAS 92:6027-6031)and provide guidance for generating the subject compound library. Bothlibraries were constructed using an orthogonal attachment strategy inwhich the library member was linked to the solid support by aphotolabile linker and the tags were attached through a linker cleavableonly by vigorous oxidation. Because the library members can berepetitively partially photoeluted from the solid support, librarymembers can be utilized in multiple assays. Successive photoelution alsopermits a very high throughput iterative screening strategy: first,multiple beads are placed in 96-well microtiter plates; second,compounds are partially detached and transferred to assay plates; third,a metal binding assay identifies the active wells; fourth, thecorresponding beads are rearrayed singly into new microtiter plates;fifth, single active compounds are identified; and sixth, the structuresare decoded.

Exemplification

The invention now being generally described, it will be more readilyunderstood by reference to the following examples, which are includedmerely for purposes of illustration of certain aspects and embodimentsof the present invention, and are not intended to limit the invention.

EXAMPLE 1 Synthesis of a Series of Novel Piperidine MonoamineTransporter Ligands

Our proprietary piperidine monoamine transporter ligands, while sharinga structure activity relationships with the related tropanes, are morereadily prepared in isomeric and enantiomeric forms allowing us accessto a large range of monoamine selectivities. As this selectivity ishighly dependant on a number of factors including the orientation of theC-3 ester, as well as the absolute configuration of the ligand, we willprepare both enantiomers of each isomer (Scheme 2) under the conditionsutilized in the preliminary studies. The trans-(+) isomer [(+)-10] isreadily prepared from the corresponding cis-(−) isomer [(−)-1] by thebase catalysed epimerization.⁸

Based on preliminary studies in which the “3+1” methodology was employedutilizing the N-propylthiol analog of MTPT demonstrated excellent brainuptake, we will prepared a second series of compounds with the N₂S₂chelating unit tethered to the nitrogen of the piperidine as shown isScheme 3. The required N-chloropropyl analogs have been previouslyprepared in our laboratories and are available in excellent yield. It isanticipated that the relatively unhindered chloride can be directlyalkylated with the PMB protected N₂S₂ chelate group. In the unlikelyevent that this does not prove to be possible the chelate can beconstructed in a stepwise manner similar to that used for ourpreliminary studies.

EXAMPLE 2 Preparation of Rhenium-Piperidine Complexes

The properties of the Group VII metals technetium and rhenium are verysimilar due to their periodic relationship. It is anticipated that themetals will demonstrate similar reaction chemistry, which is often thecase for the thiol, nitrogen, phosphine and oxo-chemistry of these twometals. Likewise, perrhenate and pertechnetate have very similarreaction behaviors.²⁸ The similar reductions of the M(VII) oxo speciesby SnCl₂ allow for easy substitution of the nonradioactive rhenium as amodel for the medicinally useful technetium-99m, which routinely usestin reduced ^(99m)Tc. Synthesizing the rhenium-piperidine complexes willallow us a facile route to structurally characterize the products. Thecharacterized products can then be used for in vitro pharmacologicalstudies. The periodic relationship between Tc and Re further indicatesthat Tc-99m radiopharmaceuticals can be designed by modeling analogousrhenium complexes.²⁹

The synthesis of the rhenium analogs will follow the establishedchemistry of the N₂S₂ system in forming stable, neutral, rhenium-oxocomplexes.^(30,31) Our N₂S₂ system, with three easily removed protonsforms a predictable metal-complex with an overall net charge of zero.The synthesis of the Re(V) complexes will be accomplished by reacting[TBA][ReOBr₄(OPPh₃)] with the appropriate piperidine ligand in the ratioof 1:1.2 in 10 mL of methanol and three equivalents of NEt₃ as base. Thereaction will be allowed to reflux for ½ hour. After cooling thereaction products will be purified using a small column using the methodestablished by Spies and co-workers.³² Alternatively, the rhenium (V)starting material [ReOCl₃(PPh₃)₂] may be employed as the potentialrhenium starting material. This versatile material has proven successfulin the past for us in dealing with nitrogen and sulfur donoratoms.^(33,34) A schematic depiction of the reaction is illustrated inScheme 4. The synthesized rhenium-piperidine complexes will be runthrough a chiral HPLC column for separation and purification purposesfollowing recent procedures.³⁵ The complexes will then be analyzed byelemental analysis, infrared spectroscopy, mass spectroscopy, and NMRspectroscopy. Finally we will attempt to crystallize the⁹⁹Tc/Re-piperidine complexes.

Scheme 4. Synthesis of the rhenium-piperidine complexes.

EXAMPLE 3 In Vitro Pharmacological Studies on Piperidine Ligands and theCorresponding Rhenium Complexes

The pharmacological profile for each of the rhenium-oxo complexes, aswell as the free ligands will be determined by the binding affinities ateach of the monoamine transporters. The binding affinity at DAT (humanrecombinat, expressed in CHO cells) will be determined by its ability todisplace 0.15 nM [¹²⁵I]RTI-55.³⁶ The binding affinity at NET (humanrecombinat, expressed in MDCK) will also be determined by the ability ofthe complexes to displace 0.20 nM [¹²⁵I]RTI-55.³⁷ The binding affinityat 5-HTT (human recombinat, expressed in HEK-293) will be determined byits ability to displace 0.15 nM [¹²⁵I]RTI-55.³⁶ All compounds willinitially be tested at 10⁻⁶ M (in duplicate) and compounds that exhibitdisplacement of >40% will be assayed (at 10⁻⁷, 10⁻⁸, 10⁻⁹ M induplicate) and approximate IC₅₀ values are calculated.

EXAMPLE 4 Preparation and Characterization of 99mTc Labeled Versions ofHigh Affinity Piperidines

Preparation of the Tc-99m-labeled piperidine complexes will be achievedby adding 10 mCi of TcO₄ ⁻ to a 0.9% saline solution of sodiumgluceptate (200 mg/3 ml). After 20 minute incubation, 400 ul will beadded to a solution of 400 ul of sodium acetate (50 mM, pH 5.2) and theappropriate piperidine ligand (50 ug). The mixture will be heated at 80°C. for 30 min. The mixture is then extracted with ethyl acetate (3×1mL), dried over sodium sulfate, and dried under N₂. The residue is thenre-dissolved in ethanol (400 ul) and purity checked via HPLC by aHamilton PRP-1 (5 mm, 25 cm) column using CH₃CN buffer to elute thereaction products. The buffer consists of dimethylglutaric acid (0.05mM) which is then pH adjusted to 7.0 with NaOH.

As part of our preliminary studies we have already developed theproposed stability tests for ^(99m)Tc-labeled piperidine complexes. Thestability of the radiolabeled compounds in solution and in plasma willbe determined as a function of time and solution conditions such as pHand solvents. Specifically, after radiolabeling and isolation, theproduct will be allowed to sit at room temperature for 48 hours afterwhich HPLC analysis will be performed to check for degree of labelretention, as well as potential product degradation. We will analyze forthe reformation of TcO₄ ⁻ and the presence of the reduced species TcO₂.To assist in predicting the in-vivo label stability ligand challengeswill be performed. Specifically, the product will be incubated with acompeting biological ligand such as cysteine, albumin, and transferrin,testing the stability of the radiolabel via HPLC analysis. Finally wewill test the product in plasma as a function of time and pH.

EXAMPLE 5 In Vivo Rat Studies of Brain Uptake of Certain^(99m)Tc-complexes

Once pharmacological studies are complete, demonstrating the bindingaffinity of the ligands and rhenium complexes for the dopaminetransporter, and the Tc-99m labeling methods are elucidated, preliminaryrat studies will be performed. The studies will evaluate uptake andretention in the brain. The evaluations will be performed by tissuesampling at various times following administration of theTc-99m-piperidine complexes to the rats. The studies will be repeatedwith β-CIT pretreatment, which competes with dopamine transporterbinding, to determine if specific uptake can be blocked. A comparison ofbrain uptake and retention within the series, as well as with otherSPECT DAT complexes, will be performed.

EXAMPLE 6 Synthesis of(+)-4β-(4′-Chlorophenyl)-1-methylpiperidine-3β-[2-(4′-methoxybenzylthio)-ethyl)aminomethyl]-N-[2-(4′-methoxybenzylthio)ethyl)lacetaminde((+)-5)

(−) Lithium 4β-(4′-Chlorophenyl)-1-methylpiperidine-3β-carboxylate,(−)-2: A mixture of (−)-1 (Kozikowski et. al. J. Med. Chem. 1998, 41,1962-1969, 5.0 g, 19 mmol) and LiOH (670 mg, 28 mmol) inTHF/H_(2O ()2:1, 150 mL) was heated to refulx for 16 h. The resultingclear colorless solitio was then concentrated to 30 mL and washed withether (100 mL). The aqueous solution was then concentrated to afford(−)-2 as a white solid (7.28 g, quantitative) that was used as obtained.

(+) Lithium 4β-(4′-Chlorophenyl)-1-methylpiperldine-3β-carboxylate,(+)-2: Prepared as described above from (+)-1 to afford (+)-2 as a whitesolid (quantitative) that was used as obtained.

(−)-N-[2-(4′-methoxybenzylthio)ethyl]4β-(4′-Chlorophenyl)-1-methylpiperidine-3β-carboxyamide, (−)-3: To asuspension of (−)-2 (3.50 g, 8.9 mmol) in THF (50 mL) was added a 2 Msolution of HCl in anhydrous ether (25 mL). The resulting mixture wasstirred for 30 min at rt and concentrated. The residue obtained wassuspended in THF/CH₂Cl₂ (1:1, 50 mL) and oxalyl chloride (4.0 mL, 48mmol) was added dropwise. The resulting suspension was stirred at rt for2 h and the resulting yellow solution was concentrated to afford thecrude acid chloride as a yellow foam. This foam was disolved in THF (100mL) and treated with a mixture of 1-amino-2-(4′methoxybenzylthio)ethane(3.8 g, 19 mmol) and Et₃N (5.4 mL, 39 mmol). The resulting reaction wasstirred at rt for 2 h and then concentrated. The residue obtained wassuspended in saturated NaHCO₃ (75 mL) and extracted with CH₂Cl₂ (2×75mL). Flash chromatography (EtOAc/Et₃N, 9:1, SiO₂) afforded (−)-3 (2.44g, 63% from (−)-1) as a celar colorless oil: R_(f) 0.6 (EtOAc/Et₃N,9:1); [α]_(D)−71.0 (c 1.33, CHCl₃); ¹H NMR (CDCl₃) δ 1.69-1.74 (m, 1H2.06-2.18 (m, 1H), 2.23-2.36 (m, 4H), 2.56 (t, 2H, J=6.2 Hz), 2.69 (m,1H), 2.79 (dt, 1H, J=4.7, 11.0 Hz), 3.02-3.08 (m, 2H), 3.23-3.29 (m,1H), 3.43-3.51 (m, 1H), 3.69 (s, 3H), 3.80 (s, 3H), 6.85 (d, 2H, J=8.6Hz), 7.07 (d, 2H, J=9.5 Hz), 7.20 (d, 2H, J=9.5 Hz), 7.23 (d, 2H, J=8.6Hz), 8.99 (m, 1H)].

(+)-N-[2-(4′-methoxybenzylthio)ethyl]4β-(4′-Chlorophenyl)-1-methylpiperidine-3β-carboxyamide, (+)-3: Preparedas described above from (+)-2 to afford (+)-3 (8.6 g, 88% from (+)-1) asa clear colorless oil: [α]_(D)+70.4 (c 2.09, CHCl₃).

(−)-4β-(4′-Chlorophenyl)-1-methylpiperidine-3β-[2-(4′-methoxybenzylthio)ethyl)aminomethyl],(−)-4: Lithium aluminum hydride (430 mg, 11 mmol) was added portionwiseto a solution of (−)-3 (2.4 g, 5.6 mmol) in THF (50 mL). The resultingsuspension was heated to reflux for 18 h and then carefully quenchedwith 1 N aqueous NaOH (10 mL). The resulting mixture was stirred for 30min and then filtered through celite. The aqueous layer was separatedfrom the filtrates and extracted with CH₂Cl₂ (2×25 mL). The pooledorganic extracts were dried (Na₂SO₄) and concentrated. Flashchromatography (EtOAc/Et₃N, 9:1, SiO₂) afforded (−)-4 (1.3 g, 55%) as aclear viscous oil: R_(f) 0.3 (EtOAc/Et₃N, 9:1); [α]_(D)−45.9 (c 1.50,CHCl₃); ¹H NMR (CDCl₃) δ 1.69-1.77 (m, 1H), 2.02-2.11 (m, 3H), 2.18-2.28(m, 2H), 2.30 (s, 3H), 2.45-2.49 (m, 2H), 2.55-2.62 (m, 2H), 2.78-2.85(m, 2H), 3.01-3.05 (m, 1H), 3.03 (d, 1H, J=7.4 Hz), 3.59 2H), 3.78 (s,3H), 6.81 (d, 2H, J=8.6 Hz), 7.14 (d, 2H, J=8.2), 7.16 (d, 2H, J=8.6Hz), 7.27 (d, 2H, J=8.2 Hz).

(+)-462-(4′-Chlorophenyl)-1-methylpiperidine-3β-[2-(4′-methoxybenzylthio)ethyl)aminomethyl],(+)-4: Prepared as described above from (+)-3 to afford (+)-4 (2.46 g,46%) as a clear colorless oil: [α]_(D)+45.1 (c 1.74, CHCl₃),

(+)-4β-(4′-Chlorophenyl)-1-methylpiperidine-3β-[2-(4′-methoxybenzylthio)ethyl)aminomethyl]N-[2-(4′-methoxybenzylthio)ethyl)]acetaminde (+)-5: A mixture of (+)-4(1.45 g, 3.5 mmol), N-[2-(4′-methoxybenzylthio)ethyl)] 2-bromoacetamide(2.0 g, 6.9 mmol) and K₂CO₃ (1.4 g, 10 mmol) was stirred at rt in MeCN(10 mL). After 28 h the solvents were removed and the residue suspendedin saturated NaHCO₃ (50 mL) and extracted with CH₂Cl₂ (3×25 mL). Thepooled organic extracts were dried (Na₂SO₄) and concentrated. Flashchromatography (EtOAc/Et₃N, 9:1, SiO₂) afforded (+)-5 (871 mg, 38%) as aclear viscous oil: R_(f) 0.5 (EtOAc/Et₃N, 9:1); [α]_(D)+66.1 (c 1.40,CHCl₃); ¹H NMR (CDCl₃) δ 1.61-1.66 (m, 1H), 1.72-1.79 (m, 1H), 1.89-2.03(m, 3H), 2.04 (s, 2H), 2.23 (s, 3H), 2.27-2.47 (m, 4H), 2.53 (t, 2H,J=7.0 Hz), 2.66-2.83 (m, 2H), 2.86-2.95 (m, 2H), 3.13 (d, 1 H, J=8.9Hz), 3.32-3.46 (m, 2H), 3.57 (s, 2H), 3.68 (s, 2H), 3.77 (s, 3H), 3.78(s, 3H), 6.80-6.87 (m, 4H), 7.04 (d, 2H, J=8.2 Hz), 7.16 (d, 2H, J=8.2Hz), 7.23-7.27 (m, 4H), 8.10 (m, 1H).

EXAMPLE 7 Synthesis of(−)-N-4β-(4′-Chlorophenyl)-1-methylpiperidine-3-methylN-(2-Pyridyl)methylamine ((−)-7)

(−)-N-(2-Pyridyl)methyl4β-(4′-Chlorophenyl)-1-methylpiperidine-3β-carboxyamide, (−)-6: To asuspension of (−)-2 (3.7 g, 9.7 mmol) in THF (50 mL) was added a 2 Msolution of HCl in anhydrous ether (25 mL). The resulting mixture wasstirred for 30 min at rt and concentrated. The residue obtained wassuspended in THF/CH₂Cl₂ (1:1, 50 mL) and oxalyl chloride (4.5 mL, 52mmol) was added dropwise. The resulting suspension was stirred at rt for2 h and the resulting yellow solution was concentrated to afford thecrude acid chloride as a yellow foam. This foam was disolved in THF (100mL) and treated with a mixture of 2-aminomethylpyridine (1.8 mL, 18mmol) and Et₃N (5.4 mL, 39 mmol). The resulting reaction was stirred atrt for 2 h and then concentrated. The residue obtained was suspended insaturated NaHCO₃ (75 mL) and extracted with CH₂Cl₂ (3×75 mL). Flashchromatography (EtOAc/Et₃N, 9:1, SiO₂) afforded (−)-6 (1.82 g, 55% from(−)-1) as a yellow colorless oil: R_(f) 0.33 (EtOAc/Et₃N, 9:1);[α]_(D)−60.9 (c 1.21, CHCl₃); ¹H NMR (CDCl₃) δ 1.68 (dd, 1H, J=2.4, 13.3Hz), 2.05-2.12 (m, 1H), 2.26-2.37 (m, 5H), 2.74 (m, 1H), 2.77-2.80 (m,1H), 3.04-3.13 (m, 2H), 4.50 (abq, 2H), 6.97 (d, 2H, J=8.5 Hz), 7.14 (d,2H, J=8.5 Hz), 7.19 (dd, 1H, J=5.0, 7.0 Hz), 7.26 s, 1H), 7.64 (m, 1H),8.57 (d, 1 H, J=4.3 Hz), 9.45 (m, 1H)].

(+)-N-(2-Pyridyl)methyl4β-(4′-Chlorophenyl)-1-methylpiperldine-3β-carboxyamide, (+)-6: Preparedas described above from (+)-2 to afford (+)-6 (4.6 g, 68% from (+)-1) asa yellow colorless oil: [α]_(D)+60.4 (c 1.03, CHCl₃).

(−)-N-4β-(4′-Chlorophenyl)-1-methylpiperldine-3β-methylN-(2-Pyridyl)methylamine, (−)-7: Lithium aluminum hydride (400 mg, 11mmol) was added portionwise to a solution of (−)-6 (1.8 g, 5.3 mmol) inTHF (50 mL). The resulting suspension was heated to reflux for 18 h andthen carefully quenched with 1 N aqueous NaOH (10 mL). The resultingmixture was stirred for 30 min and then filtered through celite. Theaqueous layer was separated from the filtrates and extracted with CH₂Cl₂(3×25 mL). The pooled organic extracts were dried (Na₂SO₄) andconcentrated. Flash chromatography (CH₂Cl₂/EtOH/Et₃N, 7:2:1, SiO₂)afforded (−)-7 (352 mg, 20%) as a dark viscous oil: R_(f) 0.65(EtOAc/Et₃N, 9:1); [α]_(D)−39.⁴ (c 1.41, CHCl₃)

(+)-N-4β-(4′-Chlorophenyl)-1-methylpiperidine-3β-methylN-(2-Pyridyl)methylamine, (+)-7: Prepared as described above from (+)-6to afford (+)-7 (2.46 g, 46%) as a clear colorless oil: [α]_(D)+45.1 (c1.74, CHCl₃).

EXAMPLE 8 Synthesis of a Radiolabeled Piperidine Complex ((+)-14)

(−)-Methyl 4β-(4-Chlorophenyl)piperidine-3β-carboxylate (−)-9: Asolution of (−)-1 (8.9 g, 33 mmol), 1-chloroethyl chloroformate (5.4 mL,50 mmol), and K₂CO₃ (150 mg) in 1,2-dichloroethane (100 mL) was heatedto reflux for 2 h and diluted with a 1 M solution of HCl in ether (40mL) the resulting mixture was filtered through a pad of SiO₂ and the padwas washed with CH₂Cl₂ (100 mL). The combined filtrates wereconcentrated, diluted with MeOH (100 mL), and heated to reflux for 16 h.After 16 h the solvents were removed and the residual oil was suspendedin 10% HCl (150 mL), washed with EtOAc (100 mL), made basic with NH₄OHand extracted with CH₂Cl₂ (3×150 mL). The pooled CH₂Cl₂ layers wereconcentrated and subjected to chromatography (EtOAc/Et₃N, 9:1) to afford(−)-9 (6.8 g, 78%) as a clear colorless oil: R_(f)=0.15 (EtOAc/Et₃N,9:1); [α]_(D)−177 (c 0.92, EtOH); ¹H NMR (CDCl₃) δ 1.76 (dd, 1H, J=2.4,13.2 Hz), 2.04 (br s, 1H), 2.46 (ddd, 1H, J=4.4, 12.7, 18.0 Hz),2.80-2.89 (m, 2H), 3.07-3.13 (m, 2H), 3.40-3.50 (m, 2H), 3.56 (s, 3H),7.24 (d, 2H, J=8.3 Hz), 7.38 (d, 2H, J=8.3 Hz); ¹³C NMR (CDCl₃) δ 26.7,42.9, 45.7, 46.6, 49.1, 51.0, 128.3, 128.5, 132.1, 141.9, 173.8; MS m/z(%) 253 (19), 194 (37), 115 (48), 57 (100).

(+)-Methyl 4β-(4-Chlorophenyl)piperidine-3β-carboxylate (+)-9: Preparedas described above from (+)-1 to afford (+)-9 (78%) as a clear viscousoil: [α]_(D)+190 (c 1.1, EtOH).

(+)-Methyl4β-(4-Chlorophenyl)-1-(3-chloropropyl)piperidine-3β-carboxylate (+)-11:A solution of (+)-9 (1.4 g, 5.5 mmol), bromochloropropane (1.5 mL, 15mmol), and K₂CO₃ (4.1 g, 30 mmol) in acetone (100 mL) was stirred at rtfor 18 h. The reaction mixture was diluted with saturated NaHCO₃ (100mL) and extracted with ether (2×75 mL). The pooled organic extracts werewashed with water (50 mL), brine (50 mL) and dried (Na₂SO₄).Chromatography (hexanes/EtOAc, 1:1, SiO₂) afforded (+)-11 (1.5 g, 83%)as a clear colorless oil: R_(f=)0.8 (hexanes/EtOAc, 1:1); [α]_(D)+26.6(c 1.05, CHCl₃); ¹H NMR (CDCl₃) δ 1.36 (m, 1H), 1.77 (m, 1H), 1.99-2.18(M, 3H), 2.27-2.42 (m, 3H), 2.52-2.62 (m, 3H), 3.35 (m, 1H), 3.08-3.19(m, 5H), 6.96 (d, 2H, J=8.7 Hz), 7.14 (d, 2H), J=8.7 Hz). MS m/z (%) 331(3), 329 (9), 294 (12), 266 (100), 223 (27).

(+)-Methyl4β-(4-Chlorophenyl)-1-(3-[N-(trytylthio)ethyl]acetamidyl]-N-(trytylthio)ethylaminopropyl)piperidine-3β-carboxylate(+)-12: A solution of (+)-11 (260 mg, 0.79 mmol),N-(trytylthio)ethyl]acetamidyl N-(trytylthio)ethylamine (535 mg, 0.79mmol), KI (10 mg) and K₂CO₃ (140 mg, 1 mmol) in MeCN (25 mL) was heatedto reflux for 8 h. The solvents were removed and the residue wassuspended in 1/2 saturated NaHCO₃ (50 mL) and extracted with ether (3×25mL). The pooled organic extracts were dried (Na₂SO₄) and concentrated.Chromatography (hexanes/EtOAc, gradient, SiO₂) afforded (+)-12 (110 mg,14%) as a clear colorless oil: R_(f=)0.4 (EtOAc).

(+)-Methyl4β-(4-Chlorophenyl)-1-(3-[N-(trytylthio)ethyl]acetamidyl]-N-(trytylthio)ethylaminopropyl)piperidine-3β-carboxylate(+)-13: To a solution of (+)-12 (10 mg) in CH₂Cl₂ (250 μL) was added TFA(300 μL) and triethylsilane (200 μL). The solution was allowed to stirat rt for 30 minutes. The solvents were removed under a stream of N₂ andwashed with hexanes (3×1 mL). The residue of (+)-13 (6 mg, 80%) obtainedwas disolved in DMSO (600 μL).

Radiolabeling of (+)-13 with Tc-99m: [^(99m)Tc]pertechnetate (10 mCi)was added to a 0.9% saline solution of Na gluceptate (200 mg/3 mL).After 20 minutes, an alquot (400 μL) was added to a solution of NaOAc(400 μL, 50 mM, pH 5.2) and (+)-13 (1 mg =100 ul DMSO). The mixture wasincubated at room temperature for 30 minutes whereupon it was analyzedvia HPLC for product yield and purity. The HPLC was a Varian ProStar 345equipped with a Vydac C18 column. The Tc-99m-labeled piperidine complexwas eluted using a gradient (0-100% B) method with the solvents H₂O+0.1%TFA and CH₃CN+0.1% TFA. After HPLC separation, the TFA was removed usinga Waters C18 Sep-Pak and filtered through a Millipore Millex-GV 0.22 μmfilter. The final product was diluted and made isotonic by addition of0.9% saline to afford a dose (10 mL) containing 3.98 mCi of activity.HPLC analysis was performed on the dose at 3 and 24 h after preparation,the product was >90% pure at both time points.

References Cited in the Specification

-   1. Ilgin, N., Zubieta, J., Reich, S. G., Dannals, R. F., Frost J. J.    Positron Emission Tomographic Imaging of the Dopamine Transporter in    progressive supranuclear palsy and Parkinson's disease. Neurology    (1999);52(6):1221-6.-   2. Hantraye P, Brownell A-L, Elmaleh D R, Spealman R D, Wullner U,    Brownell G L, Madras B K, Isacson O. Dopamine fiber detection by    ¹¹C-CFT and PET in a primate model of Parkinsonism. NeuroReport    (1992)3:265-268.-   3. Stoof J C, Winogrodzka A, van Muiswinkel F L, Wolters E C, Voom    P, Groenewegen H J, Booij J, Drukarch B. Leads for the development    of neuroprotective treatment in Parkinson's disease and brain    imaging methods for estimating treatment efficacy. Eur J    Pharmacol (1999) 375(1-3):75-86.-   4. Innis R, Baldwin R, Sybirska E, Zea Y, Laruelle M, al-Tikriti M,    Chamey D, Zoghbi S, Smith E, Wisniewski G, et al. Single photon    emission computed tomography imaging of monoamine reuptake sites in    primate brain with [¹²³I]ClT. Eur J Pharmacol (1991)    200(2-3):369-370.-   5. Shaya E K, Scheffel U, Dannals R F, Ricaurte G A, Carroll F I,    Wagner H N Jr, Kuhar M J, Wong D F. In vivo imaging of dopamine    reuptake sites in the primate brain using single photon emission    computed tomography (SPECT) and iodine-123 labeled RTI-55.    Synapse (1992) 10(2):169-172.-   6. Neumeyer J L, Wang S Y, Milius R A, Baldwin R M, Zea-Ponce Y,    Hoffer P B, Sybirska E, al-Tikriti M, Charney D S, Malison R T, et    al. [¹²³I]-2 beta-carbomethoxy-3 beta-(4-iodophenyl)tropane:    high-affinity SPECT radiotracer of monoamine reuptake sites in    brain. J Med Chem (1991) 34(10):3144-146.-   7. Kung, H. F., Kim, H-J., Kung, M-P., Meegalla, S. K., Plossl, K.,    Lee, H-K. Imaging of dopamine transporters in humans with    technetium-99m TRODAT-1. Eur. J. Nuc. Med. (1996) 11: 1527-1530.-   8. Meegalla, S. K., Plossl, K., Kung, M.-P., Chumpradit, S.,    Stevenson, A. D., Kushner, S. A., McElgin, W. T., Mozley, D. P.,    Kung, H. F. Synthesis and characterization of technetium-99m-labeled    tropanes as dopamine transporter-imaging agents. J. Med.    Chem. (1997) 40: 9-17.-   9. Zhuang, Z-P., Mu, M., Kung, M-P., Plossl, K., Kung, H. F.    Homologue of [99mTc] TRODAT-1 as dopamine transporter imaging    agent. J. Labeled. Cpd. Radiopharm. (1999) 42:S351.(abstract)-   10. Smith, M. P., Johnson, K. M., Zhang, M., Flippen-Anderson, J.    L., Kozikowski, A. P. Tuning the selectivity of monoamine    transporter inhibitors by the stereochemistry of the nitrogen lone    pair. J. Amer. Chem. Soc. (1998) 120: 9072-9073.-   11. Hamilton, G. S., Steiner, J. P. Immunophilins: beyond    immunosuppression. J. Med. Chem. (1998)41: 5119-5143.-   12. Villemagne, V. L., Rothman, R. B., Yokoi, F., Rice, K. C.,    Matecka, D., Dannals, R. F., Wong, D. F. Doses of GBR12909 that    suppress cocaine self-administration in non-human primates    substantially occupy dopamine transporters as measured by [11C]    WIN35,428 PET scans. Synapse (1999) 32(1):44-50.-   13. Cook, E. H., Krasowski, M. D., Cox, N. J., Olkon, D. M.,    Kieffer, J. E., Leventhal, B. L. Association of attention-deficit    disorder and the dopamine transporter gene. Am. J. Hum.    Genet. (1995) 56(4): 993-998.-   14. Carroll F I, Lewin A H, Boja J W, Kuhar M J. Cocaine receptor:    biochemical characterization and structure-activity relationships of    cocaine analogues at the dopaamine transporter. J Med Chem (1992)    35(6):969-981.-   15. Fowler J S, Volkow N D, Wolf A P, Dewey S L, Schlyer D J,    Macgregor R R, Hitzemann R, Logan J, Bendriem B, Gatley S J, et al.    Mapping cocaine binding sites in human and baboon brain in vivo.    Synapse (1989) 4(4):371-377.-   16. Frost, J. J., Rosier, A. J., Reich, S. G., Smith, J. S.,    Ehlers, M. D., Snyder, S. H., Ravert, H. T., Dannals, R. F.,    Positron Emission tomographic imaging of the dopamine transporter    with [¹¹C]-WIN 35,428 reveals marked declines in mild Parkinson's    disease. Ann. Neurol. (1993) 34: 423-431.-   17. Yung, B. C. K., Dannals, R. F., Kuhar, M. J., Shaya, E. K.,    Ravert, H. T., Chen, C., Chan, B., Scheffel, U., Ricaurte, G.,    Folio, T., Wagner, H. N., Neumeyer, M., Wong, D. F. In vivo dopamine    transporter sites imaging in human using [¹¹C]-WIN35,428 positron    emission tomography (PCET) [abstract]. J. Nucl. Med. (1993) 34: 197.-   18. Innis, R. B., Seibyl, J. P., Scanley, B. E., et. al. Single    photon emission computed tomographic imaging demonstrates loss of    striatal dopamine transporters in Parkinson's disease. Proc. Natl.    Acad. Sci. USA (1993) 90: 11965-11969.-   19. Mozley, P. D., Stubbs, J. B., Kim, H. J., McElgin, W. T.,    Kung, M. P., Meegalla, S. K., Kung, H. F. Dosimetry of an    iodine-123-labeled tropane to image dopamine transporters. J. Nucl.    Med. (1996) 37: 151-159.-   20. Meegalla, S., Plossl, K., Kung, M-P., Stevenson, D. A.,    Liable-Sands, L. M., Rheingold, A. L., Kung, H. F. First example of    a 99mTc complex as a dopamine transporter Imaging agent. J. Am.    Chem. Soc. (1995) 117: 11037-11038.-   21. Kaufman M J, Madras B K. Distribution of cocaine recognition    sites in monkey brain. Synapse 1992;12:99-111.-   22. Meltzer P C, Liang A, Brownell A-L, Elmaleh D R, Madras B K.    Substituted 3-phenyltropane analogs of cocaine: synthesis,    inhibition of binding at cocaine recognition sites, and Positron    Emission Tomography Imaging. J. Med. Chem. (1993) 36,:855-862.-   23. Reedijk J., Medicinal Applications of heavy-metal compounds.    Curr. Opin. Chem. Biol. (1999) 3(2): 236-240.-   24. Hom, R. K., Katzenellenbogen, J. A. Technetium-99m-labeled    receptor-specific small-molecule radiopharmaceuticals: recent    developments and encouraging results. Nuc. Med. and Biol. (1997) 24:    485-498.-   25. Hoepping, A., Babich, J., Zubieta, J. A., Johnson, K. M.,    Machill, S., Kozikowski, A. P. Synthesis and biological evaluation    of two novel DAT-binding technetium complexes containing a    piperidine based analogue of cocaine. Bioorg. Med. Chem. Lett.    (1999) 9: 3211-3216.-   26. Warren G L, Caldwell J H, Kremer P A, et al: New iodinated    phenyl fatty acids for imaging myocardial metabolism. J. Nucl.    Med. (1986) 27: 939-940 (abstr.).-   28. Rose, D. J., Maresca, K. P., Nicholson, T., Davison, A.,    Jones, A. G., Babich, J., Fischman, A., Graham, W., DeBord, J. R.    D., Zubieta, J. Synthesis and Characterization of Organohydrazine    Complexes of Technetium, Rhenium, and Molybdenum with the    {M(η1-HXNNR)(η2-HyNNR)} Core and Their Relationship to Radiolabeled    Organohydrazine-Derivatized Chemotactic Peptides with Diagnostic    Applications. Inorg. Chem. (1998) 37: 2701-2716.-   29. Nicholson, T., Cook, J., Davison, A., Rose, D. J., Maresca K.    P., Zubieta, J. A., Jones, A. G. The synthesis and characterization    of [MCl₃(N═NC₅H₄NH)(HN═NC₅H₄N)] from [MO₄]⁻ (where M=Re, Tc)    organodiazenido, organodiazene-chelate complexes. Inorg. Chim.    Acta (1996) 252: 421-426.-   30. Kung, H. F., Yu, C. C., Billings J., Molnar, M., Blau, M.    Synthesis of New Bis(aminoethanethiol) (BAT) derivatives: Possible    ligands for 99mTc brain imaging agents. J. Med. Chem. (1985) 28:    1280-1284.-   31. Chiotellis, E., Varvarigou, A. D., Maina, T H.,    Stassinopoulou, C. I. Comparative evaluation of 99mTc-labeled    aminothiols as possible brain perfusion imaging agents. Nucl. Med.    Biol. (1988) 15: 215-223.-   32. Spies, H., Fietz, T., Pietzsch H-J., Johannsen, B., Leibnitz,    P., Reck, G., Scheller, D., Klostermann, K. Neutral oxorhenium(V)    complexes with tridentate dithiolates and monodentate alkane- or    arene-thiolate coligands. J. Chem. Soc. Dalton Trans. (1995)    2277-2280.-   33. Maresca, K. P., Bonavia, G. H., Babich, J. W., Zubieta, J. A.    Expansion of the ‘3+1’ concept of oxorhenium-thiolate chemistry to    cationic and binuclear complexes. Inorg. Chem. Comm. (1998) 1:    209-212.-   34. Rose, D. J., Maresca, K. P., Kettler, P. B., Chang, Y. D.,    Soghomonian, V., Chen, Q., Abrams, M. J., Larsen, S. K., Zubieta, J.    Synthesis and characterization of rhenium thiolate complexes.    Inorganic Chemistry (1995) 35: 3556-3562.-   35. Luyt, L. G., Jenkins, H. A., Hunter, D., H. An N2S2 bifunctional    chelator for technetium-99m and rhenium: Complexation, conjugation,    and epimerization to a single isomer. Bioconjugate Chem. (1999) 10:    470-479.-   36. Gu, H.; Wall, S. C.; Rudnick, G. Stable expression of biogenic    amine transporters reveals differences in inhibitor sensitivity,    kinetics, and ion dependence. J. Biol. Chem. (1994) 269, 7124-7130-   37. Galli, A.; DeFelice, L. J.; Duke, B. J.; Moore, K. R.;    Blakely, R. D. Sodium-dependent norepinephrine-induced currents in    norepinephrine-transporter-transfected HEK-293 cells blocked by    cocaine and antidepressants. J. Exp. Biol. (1995) 198, 2197-2212.

Incorporation By Reference

All of the patents and publications cited herein are hereby incorporatedby reference.

Equivalents

Those skilled in the art will recognize, or be able to ascertain usingno more than routine experimentation, many equivalents to the specificembodiments of the invention described herein. Such equivalents areintended to be encompassed by the following claims.

1. A compound represented by A:

wherein X represents O or (H)₂; R represents H, alkyl, alkoxyl,alkylamino, aryl, heteroaryl, aralkyl, heteroaralkyl, acyl,alkoxycarbonyl, or alkylaminocarbonyl; R₂ represents H; R₃ representsoptionally substituted aryl or heteroaryl; R₄ represents H; R₅represents independently for each occurrence H, alkyl, alkoxyl,alkylamino, aryl, heteroaryl, aralkyl, heteroaralkyl, acyl,alkoxycarbonyl, or alkylaminocarbonyl; and n is 0, 1, or
 2. 2. Thecompound of claim 1, wherein X represents O.
 3. The compound of claim 1,wherein R represents alkyl.
 4. The compound of claim 1, wherein R₃represents optionally substituted phenyl.
 5. The compound of claim 1,wherein R₅ represents H or aralkyl.
 6. The compound of claim 1, whereinn is
 1. 7. The compound of claim 1, wherein X represents O; and Rrepresents alkyl.
 8. The compound of claim 1, wherein X represents O;and R₃ represents optionally substituted phenyl.
 9. The compound ofclaim 1, wherein X represents O; and R₅ represents independently foreach occurrence H or aralkyl.
 10. The compound of claim 1, wherein Xrepresents O; and n is
 1. 11. The compound of claim 1, wherein Xrepresents O; R represents alkyl; and R₃ represents optionallysubstituted phenyl.
 12. The compound of claim 1, wherein X represents O;R represents alkyl; and R₅ represents independently for each occurrenceH or aralkyl.
 13. The compound of claim 1, wherein X represents O; Rrepresents alkyl; R₃ represents optionally substituted phenyl; and R₅represents independently for each occurrence H or aralkyl.
 14. Thecompound of claim 1, wherein X represents O; R represents methyl; R₃represents 4-chlorophenyl; R₅ represents independently for eachoccurrence H or 4-methoxybenzyl; and n is
 1. 15. A compound representedby B:

wherein X represents O or (H)₂; R represents H, alkyl, alkoxyl,alkylamino, aryl, heteroaryl, aralkyl, heteroaralkyl, acyl,alkoxycarbonyl, or alkylaminocarbonyl; R₂ represents H; R₃ represents H;R₄ represents optionally substituted aryl or heteroaryl; R₅ representsindependently for each occurrence H, alkyl, alkoxyl, alkylamino, aryl,heteroaryl, aralkyl, heteroaralkyl, acyl, alkoxycarbonyl, oralkylaminocarbonyl; and n is 0, 1, or
 2. 16. The compound of claim 15,wherein X represents O.
 17. The compound of claim 15, wherein Rrepresents alkyl.
 18. The compound of claim 15, wherein R₄ representsoptionally substituted phenyl.
 19. The compound of claim 15, wherein R₅represents H or aralkyl.
 20. The compound of claim 15, wherein n is 1.21. The compound of claim 15, wherein X represents O; and R representsalkyl.
 22. The compound of claim 15, wherein X represents O; and R₄represents optionally substituted phenyl.
 23. The compound of claim 15,wherein X represents O; and R₅ represents independently for eachoccurrence H or aralkyl.
 24. The compound of claim 15, wherein Xrepresents O; and n is
 1. 25. The compound of claim 15, wherein Xrepresents O; R represents alkyl; and P4 represents optionallysubstituted phenyl.
 26. The compound of claim 15, wherein X representsO; R represents alkyl; and R₅ represents independently for eachoccurrence H or aralkyl.
 27. The compound of claim 15, wherein Xrepresents O; R represents alkyl; R₄ represents optionally substitutedphenyl; and R₅ represents independently for each occurrence H oraralkyl.
 28. The compound of claim 15, wherein X represents O; Rrepresents methyl; R₄ represents 4-chlorophenyl; R₅ representsindependently for each occurrence H or 4-methoxybenzyl; and n is
 1. 29.A compound represented by C:

wherein X represents O or (H)₂; R represents H, alkyl, alkoxyl,alkylamino, aryl, heteroaryl, aralkyl, heteroaralkyl, acyl,alkoxycarbonyl, or alkylaminocarbonyl; R₁ represents H; R₃ representsoptionally substituted aryl or heteroaryl; R₄ represents H; R₅represents independently for each occurrence H, alkyl, alkoxyl,alkylamin6, aryl, heteroaryl, aralkyl, heteroaralkyl, acyl,alkoxycarbonyl, or alkylaminocarbonyl; and n is 0, 1, or
 2. 30. Thecompound of claim 29, wherein X represents O.
 31. The compound of claim29, wherein R represents alkyl.
 32. The compound of claim 29, wherein R₃represents optionally substituted phenyl.
 33. The compound of claim 29,wherein R₅ represents H or aralkyl.
 34. The compound of claim 29,wherein n is
 1. 35. The compound of claim 29, wherein X represents O;and R represents alkyl.
 36. The compound of claim 29, wherein Xrepresents O; and R₃ represents optionally substituted phenyl.
 37. Thecompound of claim 29, wherein X represents O; and R₅ representsindependently for each occurrence H or aralkyl.
 38. The compound ofclaim 29, wherein X represents O; and n is
 1. 39. The compound of claim29, wherein X represents O; R represents alkyl; and R₃ representsoptionally substituted phenyl.
 40. The compound of claim 29, wherein Xrepresents O; R represents alkyl; and R₅ represents independently foreach occurrence H or aralkyl.
 41. The compound of claim 29, wherein Xrepresents O; R represents alkyl; R₃ represents optionally substitutedphenyl; and R₅ represents independently for each occurrence H oraralkyl.
 42. The compound of claim 29, wherein X represents O; Rrepresents methyl; R₃ represents 4-chlorophenyl; R₅ representsindependently for each occurrence H or 4-methoxybenzyl; and n is
 1. 43.A compound represented by D:

wherein X represents O or (H)₂; R represents H, alkyl, alkoxyl,alkylamino, aryl, heteroaryl, aralkyl, heteroaralkyl, acyl,alkoxycarbonyl, or alkylaminocarbonyl; R₁ represents H; R₃ represents H;R₄ represents optionally substituted aryl or heteroaryl; R₅ representsindependently for each occurrence H, alkyl, alkoxyl, alkylamino, aryl,heteroaryl, aralkyl, heteroaralkyl, acyl, alkoxycarbonyl, oralkylaminocarbonyl; and n is 0, 1, or
 2. 44. The compound of claim 43,wherein X represents O.
 45. The compound of claim 43, wherein Rrepresents alkyl.
 46. The compound of claim 43, wherein R representsoptionally substituted phenyl.
 47. The compound of claim 43, wherein R₅represents H or aralkyl.
 48. The compound of claim 43, wherein n is 1.49. The compound of claim 43, wherein X represents O; and R representsalkyl.
 50. The compound of claim 43, wherein X represents O; and R₄represents optionally substituted phenyl.
 51. The compound of claim 43,wherein X represents O; and R₅ represents independently for eachoccurrence H or aralkyl.
 52. The compound of claim 43, wherein Xrepresents O; and n is
 1. 53. The compound of claim 43, wherein Xrepresents O; R represents alkyl; and R₄ represents optionallysubstituted phenyl.
 54. The compound of claim 43, wherein X representsO; R represents alkyl; and R₅ represents independently for eachoccurrence H or aralkyl.
 55. The compound of claim 43, wherein Xrepresents O; R represents alkyl; R₄ represents optionally substitutedphenyl; and R₅ represents independently for each occurrence H oraralkyl.
 56. The compound of claim 43, wherein X represents O; Rrepresents methyl; R₄ represents 4-chlorophenyl; R₅ representsindependently for each occurrence H or 4-methoxybenzyl; and n is
 1. 57.A compound represented by E:

wherein X represents O or S; Y represents O or S; R represents H, alkyl,alkoxyl, alkylamino, aryl, heteroaryl, aralkyl, heteroaralkyl, acyl,alkoxycarbonyl, or alkylaminocarbonyl; R₂ represents H; R₃ representsoptionally substituted aryl or heteroaryl; R₄ represents H; R₅represents H, alkyl, alkoxyl, alkylamino, aryl, heteroaryl, aralkyl,heteroaralkyl, acyl, alkoxycarbonyl, or alkylaminocarbonyl; m is 1 or 2;and n is 0, 1, or
 2. 58. The compound of claim 57, wherein X representsO.
 59. The compound of claim 57, wherein Y represents O.
 60. Thecompound of claim 57, wherein R represents alkyl.
 61. The compound ofclaim 57, wherein R₃ represents optionally substituted phenyl.
 62. Thecompound of claim 57, wherein R₅ represents H, alkyl, or aralkyl. 63.The compound of claim 57, wherein m is
 1. 64. The compound of claim 57,wherein n is
 1. 65. The compound of claim 57, wherein X represents O;and Y represents O.
 66. The compound of claim 57, wherein X representsO; and R represents alkyl.
 67. The compound of claim 57, wherein Xrepresents O; and R₃ represents optionally substituted phenyl.
 68. Thecompound of claim 57, wherein X represents O; and R₅ represents H,alkyl, or aralkyl.
 69. The compound of claim 57, wherein X represents O;and m is
 1. 70. The compound of claim 57, wherein X represents O; and nis
 1. 71. The compound of claim 57, wherein X represents O; Y representsO; R represents alkyl; and R₃ represents optionally substituted phenyl.72. The compound of claim 57, wherein X represents O; Y represents O; Rrepresents alkyl; and R₅ represents H, alkyl, or aralkyl.
 73. Thecompound of claim 57, wherein X represents O; Y represents O; Rrepresents alkyl; R₃ represents optionally substituted phenyl; and R₅represents H, alkyl, or aralkyl.
 74. The compound of claim 57, wherein Xrepresents O; Y represents O; R represents methyl; R₃ represents4-chlorophenyl; R₅ represents ethyl; m is 1; and n is
 1. 75. A compoundrepresented by F:

wherein X represents O or S; Y represents O or S; R represents H, alkyl,alkoxyl, alkylamino, aryl, heteroaryl, aralkyl, heteroaralkyl, acyl,alkoxycarbonyl, or alkylaminocarbonyl; R₂ represents H; R₃ represents H;R₄ represents optionally substituted aryl or heteroaryl; R₅ representsH, alkyl, alkoxyl, alkylamino, aryl, heteroaryl, aralkyl, heteroaralkyl,acyl, alkoxycarbonyl, or alkylaminocarbonyl; m is 1 or 2; and n is 0, 1,or
 2. 76. The compound of claim 75, wherein X represents O.
 77. Thecompound of claim 75, wherein Y represents O.
 78. The compound of claim75, wherein R represents alkyl.
 79. The compound of claim 75, wherein R₄represents optionally substituted phenyl.
 80. The compound of claim 75,wherein R₅ represents H, alkyl, or aralkyl.
 81. The compound of claim75, wherein m is
 1. 82. The compound of claim 75, wherein n is
 1. 83.The compound of claim 75, wherein X represents O; and Y represents O.84. The compound of claim 75, wherein X represents O; and R representsalkyl.
 85. The compound of claim 75, wherein X represents O; and R₄represents optionally substituted phenyl.
 86. The compound of claim 75,wherein X represents O; and R₅ represents H, alkyl, or aralkyl.
 87. Thecompound of claim 75, wherein X represents O; and m is
 1. 88. Thecompound of claim 75, wherein X represents O; and n is
 1. 89. Thecompound of claim 75, wherein X represents O; Y represents O; Rrepresents alkyl; and R represents optionally substituted phenyl. 90.The compound of claim 75, wherein X represents O; Y represents O; Rrepresents alkyl; and R₅ represents H, alkyl, or aralkyl.
 91. Thecompound of claim 75, wherein X represents O; Y represents O; Rrepresents alkyl; R₄ represents optionally substituted phenyl; and R₅represents H, alkyl, or aralkyl.
 92. The compound of claim 75, wherein Xrepresents O; Y represents O; R represents methyl; R₄ represents4-chlorophenyl; R₅ represents ethyl; m is 1; and n is
 1. 93. A compoundrepresented by G:

wherein X represents O or S; Y represents O or S; R represents H, alkyl,alkoxyl, alkylamino, aryl, heteroaryl, aralkyl, heteroaralkyl, acyl,alkoxycarbonyl, or alkylaminocarbonyl; R₁ represents H; R₃ representsoptionally substituted aryl or heteroaryl; R₄ represents H; R₅represents H, alkyl, alkoxyl, alkylamino, aryl, heteroaryl, aralkyl,heteroaralkyl, acyl, alkoxycarbonyl, or alkylaminocarbonyl; m is 1 or 2;and n is 0, 1, or
 2. 94. The compound of claim 93, wherein X representsO.
 95. The compound of claim 93, wherein Y represents O.
 96. Thecompound of claim 93, wherein R represents alkyl.
 97. The compound ofclaim 93, wherein R₃ represents optionally substituted phenyl.
 98. Thecompound of claim 93, wherein R₅ represents H, alkyl, or aralkyl. 99.The compound of claim 93, wherein m is
 1. 100. The compound of claim 93,wherein n is
 1. 101. The compound of claim 93, wherein X represents O;and Y represents O.
 102. The compound of claim 93, wherein X representsO; and R represents alkyl.
 103. The compound of claim 93, wherein Xrepresents O; and R₃ represents optionally substituted phenyl.
 104. Thecompound of claim 93, wherein X represents O; and R₅ represents H,alkyl, or aralkyl.
 105. The compound of claim 93, wherein X representsO; and m is
 1. 106. The compound of claim 93, wherein X represents O;and n is
 1. 107. The compound of claim 93, wherein X represents O; Yrepresents O; R represents alkyl; and R₃ represents optionallysubstituted phenyl.
 108. The compound of claim 93, wherein X representsO; Y represents O; R represents alkyl; and R₅ represents H, alkyl, oraralkyl.
 109. The compound of claim 93, wherein X represents O; Yrepresents O; R represents alkyl; R₃ represents optionally substitutedphenyl; and R₅ represents H, alkyl, or aralkyl.
 110. The compound ofclaim 93, wherein X represents O; Y represents O; R represents methyl;R₃ represents 4-chlorophenyl; R₅ represents ethyl; m is 1; and n is 1.111. A compound represented by H:

wherein X represents O or S; Y represents O or S; R represents H, alkyl,alkoxyl, alkylamino, aryl, heteroaryl, aralkyl, heteroaralkyl, acyl,alkoxycarbonyl, or alkylaminocarbonyl; R₁ represents H; R₃ represents H;R₄ represents optionally substituted aryl or heteroaryl; R₅ representsH, alkyl, alkoxyl, alkylamino, aryl, heteroaryl, aralkyl, heteroaralkyl,acyl, alkoxycarbonyl, or alkylaminocarbonyl; m is 1 or 2; and n is 0, 1,or
 2. 112. The compound of claim 111, wherein X represents O.
 113. Thecompound of claim 111, wherein Y represents O.
 114. The compound ofclaim 111, wherein R represents alkyl.
 115. The compound of claim 111,wherein R₄ represents optionally substituted phenyl.
 116. The compoundof claim 111, wherein R₅ represents H, alkyl, or aralkyl.
 117. Thecompound of claim 111, wherein m is
 1. 118. The compound of claim 111,wherein n is
 1. 119. The compound of claim 111, wherein X represents O;and Y represents O.
 120. The compound of claim 111, wherein X representsO; and R represents alkyl.
 121. The compound of claim 111, wherein Xrepresents O; and R₄ represents optionally substituted phenyl.
 122. Thecompound of claim 111, wherein X represents O; and R₅ represents H,alkyl, or aralkyl.
 123. The compound of claim 111, wherein X representsO; and m is
 1. 124. The compound of claim 111, wherein X represents O;and n is
 1. 125. The compound of claim 111, wherein X represents O; Yrepresents O; R represents alkyl; and R₄ represents optionallysubstituted phenyl.
 126. The compound of claim 111, wherein X representsO; Y represents O; R represents alkyl; and R₅ represents H, alkyl, oraralkyl.
 127. The compound of claim 111, wherein X represents O; Yrepresents O; R represents alkyl; R₄ represents optionally substitutedphenyl; and R₅ represents H, alkyl, or aralkyl.
 128. The compound ofclaim 111, wherein X represents O; Y represents O; R represents methyl;R₄ represents 4-chlorophenyl; R₅ represents ethyl; m is 1; and n is 1.129. A compound represented by I:

wherein X represents O or (H)₂; R represents H, alkyl, alkoxyl,alkylamino, aryl, heteroaryl, aralkyl, heteroaralkyl, acyl,alkoxycarbonyl, or alkylaminocarbonyl; R₁ represents —C(O)OR; R₂represents H; R₃ represents optionally substituted aryl or heteroaryl;R₄ represents H; R₅ represents independently for each occurrence H,alkyl, alkoxyl, alkylamino, aryl, heteroaryl, aralkyl, heteroaralkyl,acyl, alkoxycarbonyl, or alkylaminocarbonyl; and n is 1, 2, 3, 4, or 5.130. The compound of claim 129, wherein X represents O.
 131. Thecompound of claim 129, wherein R represents alkyl.
 132. The compound ofclaim 129, wherein R₃ represents optionally substituted phenyl.
 133. Thecompound of claim 129, wherein R₅ represents H or aralkyl.
 134. Thecompound of claim 129, wherein n is
 3. 135. The compound of claim 129,wherein X represents O; and R represents alkyl.
 136. The compound ofclaim 129, wherein X represents O; and R₃ represents optionallysubstituted phenyl.
 137. The compound of claim 129, wherein X representsO; and R₅ represents independently for each occurrence H or aralkyl.138. The compound of claim 129, wherein X represents O; and n is
 3. 139.The compound of claim 129, wherein X represents O; R represents alkyl;and R₃ represents optionally substituted phenyl.
 140. The compound ofclaim 129, wherein X represents O; R represents alkyl; and R₅ representsindependently for each occurrence H or aralkyl.
 141. The compound ofclaim 129, wherein X represents O; R represents alkyl; R₃ representsoptionally substituted phenyl; and R₅ represents independently for eachoccurrence H or aralkyl.
 142. The compound of claim 129, wherein Xrepresents O; R represents methyl; R₃ represents 4-chlorophenyl; R₅represents independently for each occurrence H or triphenylmethyl; and nis
 3. 143. A compound represented by J:

wherein X represents O or S; Y represents O or S; R represents H, alkyl,alkoxyl, alkylamino, aryl, heteroaryl, aralkyl, heteroaralkyl, acyl,alkoxycarbonyl, or alkylaminocarbonyl; R₁ represents —C(O)OR; R₂represents H; R₃ represents optionally substituted aryl or heteroaryl;R₄ represents H; R₅ represents H, alkyl, alkoxyl, alkylamino, aryl,heteroaryl, aralkyl, heteroaralkyl, acyl, alkoxycarbonyl, oralkylaminocarbonyl; m is 1 or 2; and n is 0, 1, or
 2. 144. The compoundof claim 143, wherein X represents O.
 145. The compound of claim 143,wherein Y represents O.
 146. The compound of claim 143, wherein Rrepresents alkyl.
 147. The compound of claim 143, wherein R₃ representsoptionally substituted phenyl.
 148. The compound of claim 143, whereinR₅ represents H, alkyl, or aralkyl.
 149. The compound of claim 143,wherein m is
 1. 150. The compound of claim 143, wherein X represents O;and Y represents O.
 151. The compound of claim 143, wherein X representsO; and R represents alkyl.
 152. The compound of claim 143, wherein Xrepresents O; and R₃ represents optionally substituted phenyl.
 153. Thecompound of claim 143, wherein X represents O; and R₅ represents H,alkyl, or aralkyl.
 154. The compound of claim 143, wherein X representsO; and m is
 1. 155. The compound of claim 143, wherein X represents O; Yrepresents O; R represents alkyl; and R₃ represents optionallysubstituted phenyl.
 156. The compound of claim 143, wherein X representsO; Y represents O; R represents alkyl; and R₅ represents H, alkyl, oraralkyl.
 157. The compound of claim 143, wherein X represents O; Yrepresents O; R represents alkyl; R₃ represents optionally substitutedphenyl; and R₅ represents H, alkyl, or aralkyl.
 158. The compound ofclaim 143, wherein X represents O; Y represents O; R represents methyl;R₃ represents 4-chlorophenyl; R₅ represents ethyl; and m is
 1. 159. Acomplex, comprising a radionuclide; and a compound of claim 1, 15, 29,43, 57, 75, 93, 111, 129, or
 143. 160. The complex of claim 159, whereinthe radionuclide is technetium.
 161. A method of imaging brain tissue ofa mammal, comprising the step of administering to a mammal a sufficientamount of a complex of claim
 159. 162. The method of claim 161, whereinthe radionuclide is technetium.
 163. A method of imaging dopaminetransporters in brain tissue of a mammal, comprising the step ofadministering to a mammal a sufficient amount of a complex of claim 159.164. The method of claim 163, wherein the radionuclide is technetium.